Cellular Targeted Label Delivery System

ABSTRACT

The present invention relates to an isolated cellular targeted delivery system comprising a CD45+ leukocyte cell comprising within said cell a complex of one or more iron binding proteins and/or a label as well as methods for producing such isolated cellular targeted delivery system and uses of such system for therapy diagnosis and in particular for diagnosis of cancer, particularly metastatic cancer, in particular for therapy of cancer.

The present invention relates to an isolated cellular targeted delivery system comprising a CD45⁺ leukocyte cell comprising within said cell a complex of one or more iron binding proteins and/or a label as well as methods for producing such isolated cellular targeted delivery system and uses of such system for diagnosis and in particular for diagnosis of cancer, particularly metastatic cancer.

BACKGROUND OF THE INVENTION

Current imaging tools are capable of detecting large metastases (larger than 0.5-1 cm in size). However, they rarely detect the early spread of metastatic tumour cells. Human metastases smaller than 0.5 cm are avascular so without proper blood and oxygen supply. It means that the delivery of contrast agents through the blood circulation for the purpose of labelling these metastases and imaging them is not possible. The presence of hypoxia is a common characteristic of micrometastases where hypoxic fraction may be as high as 90% with little or no blood perfusion (Li, et al. 2012, Journal of Solid Tumours, 2(2): 28-33). Thus, severe hypoxia is considered as a general feature of micro-metastases.

The targeting of one or more micrometastases hidden within a large population of normal cells presents a unique challenge since access to the micrometastases is impeded by several bio-barriers, poor blood supply, further obstacles are presented by small size of the micrometastases and their dispersion to organs.

For the same reason micrometastases are often refractive to therapy. While the solid tumours from which the micrometastases have originated often respond well to conventional therapy there is often regrowth at the site of the primary tumour or at sites of metastasis. This constitutes a serious problem in clinical oncology (Muthana, et al. 2012, Cancer Res; 73(2); 490-495). It is related to characteristics of the microenvironment of solid tumours that limit drug penetration, thereby exposing the tumour to lower than efficacious concentrations of drugs (Hobbs, et al. 1998, Proc Natl Acad Sci USA: 4607-4612). This is caused by inadequate vasculature resulting in: high heterogeneity of cancer cells, low oxygen tension (hypoxia), low pH and low glucose concentration within the mass (Kizaka-Kondoh, et al., 2003, Cancer Sci 94(12):1021-1028). Additionally, rapid tumour cell proliferation in some areas might outpace the rate of new blood vessel growth, promoting formation of hypoxic area (Lewis and Murdoch, 2005, Am J Pathol 167(3):627-635). This abnormal vessel architecture and, subsequently, their impaired function resulting in tumour hypoxia is associated with a more malignant phenotype and poor survival in patients suffering from solid tumours and results in both treatment failure due to decreased drug uptake and hypoxia-inducible changes in cancer cells (Sun, et al., 2012, Clin Cancer Res 18(3):758-770; Sullivan, et al., 2008 Mol Cancer Ther 7(7):1961-1973; Kizaka-Kondoh, et al., 2003, Cancer Sci 94(12):1021-1028). Moreover, chemotherapy or radiotherapy causes additional formation of large areas of tumour hypoxia thus making the treatment of tumour even more difficult. The fact that the efficacy of anticancer therapy is limited by the presence of hypoxic tumour cells has resulted in the introduction of variety of therapeutic approaches aimed at overcoming this problem.

The present inventors have discovered that CD45⁺ leukocyte cells, in particular activated macrophages, can uptake one or more labels complexed or not with one or more iron binding proteins in vitro and deliver these complexes to or into cells, preferably to or into tumour cells in vivo. Based on this observation the present inventors have overcome one or more of the above stated problems of the prior art. Thus, the targeted delivery system of the present invention provides inta alia one or more of the following advantages: (i) specific delivery of one or more labels to tissues that attract above mentioned CD45⁺ leukocytes, preferably into diseased cells, (ii) protection of labels from inactivation in the blood circulation or clearance from the body, (iii) delivery of labels to, preferably into cells of poorly or non-vascularized areas of disease, e.g. metastases, hypoxic areas within larger tumours, rheumatic lesions, avascular wounds, skin, (iv) reduced toxicity of labels, (v) delivery of labels with poor pharmacokinetics, (vi) reduced side effects of the labels due to their targeted delivery, (vii) higher diagnostic efficacy with lower doses of the labels due to targeted delivery; (viii) lower risk of local tissue injury at the site of label administration due to administration of the label linked with iron-binding protein, which is loaded inside the CD45⁺ leukocyte; and/or (ix) possibility to detect highly hypoxic small metastases (Perez-Herrero E, Fernández-Medarde A. 2015, Eur J Pharm Biopharm 93:52-79).

SUMMARY OF THE INVENTION

In a first aspect the present invention relates to an isolated targeted delivery system comprising a CD45⁺ leukocyte cell, which is preferably capable of internalizing an iron binding protein comprising within said cell a complex of one or more iron binding proteins and one or more labels.

In a second aspect the present invention relates to an isolated targeted delivery label system comprising a CD45⁺ leukocyte cell, preferably capable of being labelled, comprising one or more labels, preferably radiolabels or their conjugates and combinations.

In a third aspect the present invention relates to a method of preparation of the isolated targeted delivery system of the first aspect of the invention comprising steps of:

-   -   a) providing, preferably purified, iron binding protein;     -   b) covalently or non-covalently linking a label to and/or         encapsulating a label in an iron binding protein;     -   c) providing a CD45⁺ leukocyte cell; and     -   d1) incubating the CD45⁺ leukocyte cell in the presence of the         complex of the iron binding protein and the label produced in         step b) until the CD45⁺ leukocyte cell is at least partially         loaded with the complex of the iron binding protein and the         label produced in step b) and/or     -   d2) incubating CD45⁺ leukocyte cell in the presence of the label         until the CD45⁺ leukocyte cell is at least partially labelled         with the label.

In a fourth aspect the present invention relates to an isolated targeted delivery system of the first aspect of the invention or producible according to the method of the third aspect of the invention for use as a diagnostic.

In a fifth aspect the present invention relates to a diagnostic composition comprising the isolated targeted delivery system of the first aspect of the present invention or producible according to the method of the third aspect of the invention and a pharmaceutically acceptable carrier and/or suitable excipient(s).

In a sixth aspect the present invention relates to the isolated targeted delivery system of the first aspect of the present invention or producible according to the method of the third aspect of the invention for use in diagnosing tumours, preferably a solid tumour and/or its metastases, preferably breast cancer, pancreatic cancer, bladder cancer, lung cancer, colon cancer or its metastases, or a tumour having hypoxic areas, inflammatory diseases or ischemic areas, in particular in skin wounds or after organ infarctus (heart) or ischemic retina.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before the present invention is described in detail below, it is to be understood that this invention is not limited to the particular methodology, protocols and reagents described herein as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

In the following, the elements of the present invention will be described. These elements are listed with specific embodiments, however, it should be understood that they may be combined in any manner and in any number to create additional embodiments. The variously described examples and preferred embodiments should not be construed to limit the present invention to only the explicitly described embodiments. This description should be understood to support and encompass embodiments which combine the explicitly described embodiments with any number of the disclosed and/or preferred elements. Furthermore, any permutations and combinations of all described elements in this application should be considered disclosed by the description of the present application unless the context indicates otherwise.

Several documents are cited throughout the text of this specification. Each of the documents cited herein (including all patents, patent applications, scientific publications, manufacturer's specifications, instructions, etc.), whether supra or infra, are hereby incorporated by reference in their entirety. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention.

DEFINITIONS

To practice the present invention, unless otherwise indicated, conventional methods of chemistry, biochemistry, and recombinant DNA techniques are employed which are explained in the literature in the field (cf., e.g., Molecular Cloning: A Laboratory Manual, 2^(nd) Edition, J. Sambrook et al. eds., Cold Spring Harbor Laboratory Press, Cold Spring Harbor 1989).

Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents, unless the content clearly dictates otherwise.

The term “targeted label delivery” or “targeted contrast agent delivery” refers to the delivery of a label, in particular a contrast agent to a patient or a person to be diagnosed which results in an increased concentration of the label, in particular the contrast agent in a particular region of the body when compared to other regions of the body of that patient. Preferably, the relative concentrations are compared between the diseased region(s) of the body and other regions of the body having similar access to the blood circulation. In preferred embodiments the concentration of the label, in particular a contrast agent in a given number of cells or a given biopsy volume from the diseased region is at least 10% higher, if compared to the identical number of cells or biopsy volume from a non-diseased region after administration of the targeted delivery system of the present invention, preferably after 1-24 hrs. More preferably, the concentration of the label, in particular the contrast agent in the diseased region of the body of a patient is at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70% at least 80%, at least 90%, at least 100%, at least 150%, at least 200%, at least 250%, at least 300%, at least 350%, at least 400%, at least 450%, at least 500%, more preferably at least 1000% higher than in a non-diseased region of the body after administration of the targeted delivery system of the present invention, preferably after 2-24 hrs. When assessed on the basis of total body distribution it is preferred that at least 5% of the label, in particular the contrast agent administered to a patient or a person to be diagnosed is delivered to the diseased region of the body, preferably at least 10%, more preferably at least 15%. The targeted delivery of the label, in particular the contrast agent limits the potential deleterious effects of an label, in particular the contrast agent to the diseased region of the body.

The terms “targeted label delivery system” or “targeted delivery system” are used synonymously in the present application and refer to a system that is capable of delivering a label, in particular a contrast agent to the targeted region, i.e. of capable of targeted delivery, preferably within the body of a patient.

The term “label” as used in the context of the present invention refers to any kind of compound being suitable for diagnostic purposes. Preferred compounds are selected from a fluorescent dye, a radioisotope and a contrast agent. A contrast agent is a dye or other substance that helps to show abnormal areas inside the body. In one embodiment the term label refers to a compound that comprises a chelating agent which forms a complex with divalent or trivalent metal cations. Preferred radioisotopes/fluorescence emitting isotopes are selected from the group consisting of alpha radiation emitting isotopes, gamma radiation emitting isotopes, Auger electron emitting isotopes, X-ray emitting isotopes, fluorescent isotopes, such as ⁶⁵Tb, fluorescence emitting isotopes, such as ¹⁸F, ⁵¹Cr, ⁶⁷Ga, ⁶⁸Ga, ¹¹In, ^(99m)Tc, ¹⁴⁰La, ¹⁷⁵Yb, ¹⁵³Sm, ¹⁶⁶Ho, ⁸⁸Y, ⁸⁹Zr, ⁹⁰Y, ¹⁴⁹Pm, ¹⁷⁷Lu, ⁴⁷Sc, ¹⁴²Pr, ¹⁵⁹Gd, ²¹²Bi, ⁷²As, ⁷²Se, ⁹⁷Ru, ¹⁰⁹Pd, ¹⁰⁵Rh, ^(101m15)Rh, ¹¹⁹Sb, ¹²⁸Ba, ¹²³I, ¹²⁴I, ¹³¹I, ¹⁹⁷Hg, ²¹¹At, ¹⁶⁹Eu, ²⁰³Pb, ²¹²Pb, ⁶⁴Cu, ⁶⁷Cu, ¹⁸⁸Re, ¹⁸⁶Re, ¹⁹⁸Au and ¹⁹⁹Ag as well as conjugates and combinations of above with proteins, peptides, small molecular inhibitors, antibodies or other compounds, e.g. ¹⁸F fluorodeoxyglucose (¹⁸F-FDG) or ⁶⁴Cu-porfirin. Preferred fluorescent dyes are selected from the following classes of dyes: Xanthens (e.g. Fluorescein), Acridines (e.g. Acridine Yellow), Oxazines (e.g. Oxazine 1), Cynines (e.g. Cy7/Cy 3), Styryl dyes (e.g. Dye-28), Coumarines (e.g. Alexa Fluor 350), Porphines (e.g. Chlorophyll B), Metal-Ligand-Complexes (e.g. PtOEPK), Fluorescent proteins (e.g APC, R-Phycoerythrin), Nanocrystals (e.g QuantumDot 705), Perylenes (e.g. Lumogen Red F300) and Phtalocyanines (e.g. IRDYE™700DX) as well as conjugates and combinations of these classes of dyes or fluorescent ⁶⁵Tb emitting. Preferred contrast agents are selected from paramagnetic agents, e.g. Gd, Eu, W and Mn, preferably complexed with a chelating agent. Further options are superparamagnetic iron (Fe) complexes and particles, compounds containing atoms of high atomic number, i.e. iodine for computer tomography (CT), microbubbles and carriers such as liposomes that contain these contrast agents.

The term “peptide” or “polypeptide” is used interchangeably in the context of the present invention to refer to a chain of at least two amino acids linked by peptide bonds. Thus, the term “peptide” in the context of the present invention is also used to refer to amino acid chains with more than 50, more than 100 or more than 150 amino acids.

The term “sequence identity” is used throughout the specification with regard to polypeptide and nucleotide sequence comparisons. In case where two sequences are compared and the reference sequence is not specified in comparison to which the sequence identity percentage is to be calculated, the sequence identity is to be calculated with reference to the longer of the two sequences to be compared, if not specifically indicated otherwise. If the reference sequence is indicated, the sequence identity is determined on the basis of the full length of the reference sequence indicated by SEQ ID, if not specifically indicated otherwise. For example, a polypeptide sequence consisting of 200 amino acids compared to a reference 300 amino acid long polypeptide sequence may exhibit a maximum percentage of sequence identity of 66.6% (200/300) while a sequence with a length of 150 amino acids may exhibit a maximum percentage of sequence identity of 50% (150/300). If 15 out of those 150 amino acids are different from the respective amino acids of the 300 amino acid long reference sequence, the level of sequence identity decreases to 45%. The similarity of nucleotide and amino acid sequences, i.e. the percentage of sequence identity, can be determined via sequence alignments. Such alignments can be carried out with several art-known algorithms, preferably with the mathematical algorithm of Karlin and Altschul (Karlin & Altschul (1993) Proc. Natl. Acad. Sci. USA 90: 5873-5877), with hmmalign (HMMER package, http://hmmer.wustl.edu/) or with the CLUSTAL algorithm (Thompson, J. D., Higgins, D. G. & Gibson, T. J. (1994) Nucleic Acids Res. 22, 4673-80) available e.g. on http://www.ebi.ac.uk/Tools/clustalw/ or on http://www.ebi.ac.uk/Tools/clustalw2/index.html or on http://npsa-pbil.ibcp.fr/cgi-bin/npsa_automat.pl?page=/NPSA/npsa_clustalw.html. Preferred parameters used are the default parameters as they are set on http://www.ebi.ac.uk/Tools/clustalw/ or http://www.ebi.ac.uk/Tools/clustalw2/index.html. The grade of sequence identity (sequence matching) may be calculated using e.g. BLAST, BLAT or BlastZ (or BlastX). BLAST protein searches are performed with the BLASTP program, score=50, word length=3. To obtain gapped alignments for comparative purposes, Gapped BLAST is utilized as described in Altschul et al. (1997) Nucleic Acids Res. 25: 3389-3402. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs are used. Sequence matching analysis may be supplemented by established homology mapping techniques like Shuffle-LAGAN (Brudno M., Bioinformatics 2003b, 19 Suppl 1:154-162) or Markov random fields. Structure based alignments for multiple protein sequences and/or structures using information from sequence database searches, available homologs with 3D structures and user-defined constraints may also be used (Pei J, Grishin NV: PROMALS: towards accurate multiple sequence alignments of distantly related proteins. Bioinformatics 2007, 23:802-808; 3DCoffee@igs: a web server for combining sequences and structures into a multiple sequence alignment. Poirot O, Suhre K, Abergel C, O'Toole E, Notredame C. Nucleic Acids Res. 2004 Jul. 1;32:W37-40.). When percentages of sequence identity are referred to in the present application, these percentages are calculated in relation to the full length of the longer sequence, if not specifically indicated otherwise.

The term “leukocyte” is used in the context of the present invention to refer to cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All leukocytes are produced and derived from multipotent cells in the bone marrow known as a hematopoietic stem cells. Leukocytes are found throughout the body, including the blood and lymphatic system. All leukocytes have nuclei, which distinguishes them from the other blood cells, the anucleated red blood cells (RBCs) and platelets. Types of leukocyte can be classified in standard ways. Two pairs of the broadest categories classify them either by structure (granulocytes or agranulocytes) or by cell division lineage (myeloid cells or lymphoid cells). These broadest categories can be further divided into the five main types: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. These types are distinguished by their physical and functional characteristics. Monocytes and neutrophils are phagocytic. Further subtypes can be classified; for example, among lymphocytes, there are B cells, T cells, and NK cells. Granulocytes are distinguished from agranulocytes by their nucleus shape (lobed versus round, that is, polymorphonuclear versus mononuclear) and by their cytoplasm granules (present or absent, or more precisely, visible on light microscopy or not thus visible). The other dichotomy is by lineage: Myeloid cells (neutrophils, monocytes, eosinophils and basophils) are distinguished from lymphoid cells (lymphocytes) by hematopoietic lineage (cellular differentiation lineage).

The present inventors have observed that CD45⁺ expression is characteristic of leukocyte cells that are suitable to be used in the context of the targeted delivery system of the present invention, in particular since CD45⁺ leukocyte cells are attracted to particular tissues and cells within the body and are capable of delivering complexes of one or more iron binding proteins and one or more labels, in particular the contrast agents to or into cells. It is understood by the skilled person that CD45⁺ leukocyte cells unless of clonal origin are a mixed population of different leukocytes which share the common property of expressing CD45⁺ surface antigen. Accordingly, subpopulations of cells within the diverse group of CD45⁺ leukocytes are characterized throughout the specification by further functional and/or structural characteristics. The term “CD45⁺” indicates that the majority of cells within a population of cells or essentially all cells express the CD45⁺ surface antigen. In this context and also with reference to other cellular surface antigens, the term “expresses” indicates that the surface antigen is produced within the cell and detectably exposed on the surface of a cell. The level of expression and, thus the number of surface antigens detectably exposed on the surface of a cell can vary greatly among different leukocytes. Generally, a cell is considered to be positive, i.e. is indicated to be “⁺”, for a cellular surface antigen, if at least 5, preferably at least 10 copies of the surface antigen are detectably exposed on the surface of the cell. The skilled person is well aware of how to detect, quantify and select for cells, which are positive (or negative) for a given cellular surface antigen. Preferred methods include Fluorescence

Activated Cell Sorting (FACS). In this technology fluorescently labelled antibodies are used to bind to cellular surface antigens of a population of cells, the cells are subsequently isolated into single cells and based on fluorescence intensity measured for the single cell, characterized as being positive or negative for the given cellular surface antigen. In some embodiments of the present invention it is indicated that the expression of a given protein is high or low. This means that the protein is detectably expressed in both instances, i.e. is “⁺”, however, at different levels. High and low expression, respectively, will mean different absolute numbers of proteins per cell for different proteins. Thus, a given protein may be considered to be expressed at high levels if there are more than 500 detectable copies of that protein per cell and to be expressed at low levels if there are between 1 to 50 detectable copies of that protein per cell. However, another protein may be considered to be expressed at high levels, if there are more than 5000 detectable copies and expressed at low levels, if there are between 1 to 500 detectable copies per cell. It is well known in the art how to quantify the number of proteins expressed or produced in a cell using flow cytometry and Becton Dickinson Quantibrite™ bead method (see e.g. Pannu, K. K., 2001, Cytometry. 2001 Dec. 1;45(4):250-8) or mass spectrometry (see, e.g. Milo, R., 2013, Bioessays, 35(12): 1050-1055). For the purpose of the present invention the term “high expression” of a given protein refers to detectable expression of that protein that is at least 70% of the highest expression level found, i.e. number of copies per cell, in a population of healthy CD45⁺ leukocytes. The term “low expression” of a given protein refers to detectable expression of that protein that is 30% or less of the highest expression level found, i.e. number of copies of that protein per cell, in a population of healthy CD45⁺ leukocytes. Preferably, the “highest expression level” is determined as the average of the highest expression levels found in healthy CD45⁺ leukocytes of different subjects. In some embodiments preferred subpopulations of cells are characterized as “producing” a given protein. This is understood to mean that the protein is not necessarily detectable on the surface of the cell but may only be present inside the cell. The skilled person is well aware how to detect and/or quantify production of a protein inside a cell and/or select cells producing such proteins.

The term “differentiated monocyte” is used in the context of the present invention to refer to a monocyte differentiated from the committed precursor termed macrophage-DC precursor (MDP) mainly resident in bone marrow (but could be also in the spleen) and differentiate into either dendritic cells or macrophages. In mice they consist of two main subpopulations: (i) CD11b⁺ cell with high expression of CX3CR1, low expression of CCR2 and Ly6C⁻ and (ii) CD11b⁺ cell with low expression of CX3CR1, high expression of CCR2 and Ly6C⁺. After leaving the bone marrow, mouse Ly6C⁺ monocytes differentiate into Ly6C⁻ monocytes in circulation. Similarly, in human monocyte differentiation, it is accepted that CD14⁺⁺ classical monocytes leave bone marrow and differentiate into CD14⁺⁺CD16⁺ intermediate monocytes and sequentially to CD14⁺CD16⁺⁺ non-classical monocytes in peripheral blood circulation (Yang et al. 2014; Biomark Res 2(1) doi. 10.1186/2050-7771-2-1).

Macrophages are tissue-resident professional phagocytes and antigen-presenting cells (APC), which differentiate from circulating peripheral blood monocytes (PBMs). The term “activated macrophage” is used in the context of the present invention to refer to any macrophage that is polarized. Macrophage activation is in general achieved by incubation with interleukins, cytokines and/or growth factors. In particular IL-4 and M-CSF can be used as activating agents. Activated macrophages of different phenotypes are classified into M1-macrophages, classically activated macrophages (CAM) and M2-macrophages, alternatively activated macrophages (AAM). The classically activated M1-macrophages comprise immune effector cells with an acute inflammatory phenotype. These are highly aggressive against bacteria and produce large amounts of lymphokines (Murray, and Wynn, 2011, J Leukoc Biol, 89(4):557-63). The alternatively activated, anti-inflammatory M2-macrophages can be separated into at least three subgroups. These subtypes have various different functions, including regulation of immunity, maintenance of tolerance and tissue repair/wound healing.

The term “M1 inducer” is used in the context of the present invention to refer to a compound that directs differentiation of PBMs to macrophages of the M1 type. The term “M2 inducer” is used in the context of the present invention to refer to a compound that directs differentiation of PBMs to macrophages of the M2 type. The skilled person is aware of a large number of ways to promote differentiation into either M1 or M2 macrophages.

The term “phagocytosis by macrophages” is the process by which a macrophage engulfs a solid particle to form an internal vesicle known as a phagosome.

The term “iron binding protein” as used refers to a protein that non-covalently binds an iron ion. Examples of such proteins comprise ferritin, haemoglobin, transferrin; and lactoferrin. Iron binding proteins are bound by cellular surface receptors which facilitate the internalization of these proteins into cells.

In a first aspect the present invention relates to an isolated targeted delivery label system comprising a CD45⁺ leukocyte cell, preferably capable of internalizing an iron binding protein, comprising within said cell a complex of one or more iron binding proteins and one or more labels, in particular the contrast agents.

It has been surprisingly found by the present inventors that CD45⁺ leukocytes, preferably monocytes or activated monocytes and macrophages, preferably activated macrophages, preferably M1 macrophages, more preferably M2 macrophages acquire label and deliver the label in the amount enough to be detected using imaging systems to allowing them to be used to trace their location in the body. In case of ¹⁸F-FDG this was particularly preferable in case of monocytes and activated monocytes, macrophages, activated macrophages, preferably M1 macrophages and most preferably M2 macrophages. Administration of cells-loaded with a label (¹⁸F-FDG), preferably radioactive label can visualize organ with accumulation of the labelled cells preferably by positron emission tomography (PET) imaging. Accordingly, in a second aspect the present invention relates to an isolated targeted delivery label system comprising a CD45⁺ leukocyte cell, preferably capable of being labelled with one or more labels, preferably radiolabels or their conjugates and combinations. It is a preferred embodiment of the second aspect of the present invention that the cell is directly linked or labelled with label. The label maybe within said cell, or on its surface, preferably it is on the surface of the cell.

The following preferred embodiments in each case further specify both the first and second aspect of the present invention.

The ability of a given CD45⁺ leukocyte cell or cell population to internalize iron binding proteins depends on the expression of receptors involved in this internalization process. Receptors that lead to internalization of ferritin comprise, e.g. TfR, CXCR4, CD163, and TIM-2. The skilled person is well aware how to measure the amount of uptake of an iron binding protein and preferred method of measuring the uptake are described in the Example Section below. The present inventors also noted that subpopulations of CD45⁺ leukocyte cells have a certain propensity to internalize one iron binding protein over another iron binding protein and, thus can attain higher complex concentrations and/or show less leakage of the complex from the cells. Such CD45⁺ leukocyte subpopulations are described in more detail below.

The phrase “complex of one or more iron binding proteins and an label” as used in the context of the present invention refers to a composition in which one or more molecules of the label are covalently or non-covalently bound to one or more iron binding proteins. The covalent or non-covalent binding between the one or more iron binding proteins and the one more label can be direct or indirect. In the latter case the label is linked to the iron binding protein via a linker or spacer. Linker or spacers are known to the skilled artisan, such as polyalanine, polyglycin, carbohydrates, (CH₂)n groups or polypeptide linkers. The skilled artisan will, thus, be able to select the respective suitable linker(s) or spacer(s) depending on the respective application. If the iron binding proteins form cages like, e.g. ferritin, than the term “complex” also encompasses the enclosure of label within the cage even in the absence of a covalent or non-covalent bond between the protein(s) and the active compound(s). The formation of the complex allows the transport of the label into the cell when the cell is internalizing the iron binding protein. Thus, it is preferred that the label are bound to the iron binding protein in a way that does not interfere with the transport mechanism. This can be easily tested by the skilled person using uptake assays known in the art and described in the Example Section below. It is preferred that the complex is sufficiently stable to survive the transport within the cell to the target region within the body. Thus, it is preferred that the complex rather than the label alone is delivered to the cells or into the cells in the target region. This property also reduces possible deleterious effects, e.g. cytotoxicity, of the label to the CD45⁺ leukocyte. If label are covalently coupled to the iron binding proteins such coupling is preferably through amino acids residues known to be located in surface areas that are not involved in binding to the cellular receptors required for cellular uptake of the iron binding proteins. Iron binding proteins used in the context of the present invention can form stable non-covalently bound complexes with a wide variety of labels.

The CD45⁺ leukocyte originate from the patient to be treated in such case the cell loaded with the complex would be autologous to the patient. It is also envisioned that patients are MHC typed prior to treatment with the targeted delivery of the present invention and that the leukocyte cell type used for a given patient is MHC matched to the patient. In these two preferred embodiments the CD45⁺ leukocyte is a primary cell or derived by a low number of differentiation steps from a primary cell. Alternatively, the CD45⁺ leukocyte may be from an immortalized but preferably non-transformed CD45⁺ leukocyte cell line. Thus the blood used for CD45⁺ leukocyte, preferably macrophage isolation is preferably obtained from the patient to be treated or healthy donor. Alternatively the blood can be obtained from the blood bank. Use of umbilical cord blood is also considered herein.

The present inventors noted that a subpopulation of CD45⁺ leukocytes, which are producible from a CD34⁺ hematopoietic precursor cell are particular suitable for target specific delivery of the label. Accordingly, it is preferred that the leukocytes used to produce the target delivery system are derived from CD34⁺ hematopoietic precursor cells. The skilled person is well aware how to select CD34⁺ hematopoietic precursor cells and how to differentiate such cells into leukocytes. Preferably, the CD45⁺ leukocyte is selected from the group consisting of a monocyte, a differentiated monocyte, lymphocyte and a granulocyte. Preferred subpopulations in these general categories of leukocytes are defined in the following by structural parameters, e.g. presence or absence of a given protein, functional properties and/or method of their production/differentiation. As outlined above, the targeted delivery system of the present invention still provides the advantages outlined above, if in a population of cells not every cell has a particular property in as long as the majority of cells within that population has that property. Thus, in the following the property of one preferred cell of the targeted delivery system of the present invention is described. It is appreciated by the skilled person that a pharmaceutical composition of the present invention will comprises millions of cells and that not every cell within the population will have the functional and/or structural properties outlined herein but that the pharmaceutical composition can nevertheless be used to treat a disease, if the majority of cells share the respective functional and/or structural properties.

The present inventors have recognized that subpopulations of CD45⁺ leukocytes have particular advantageous properties including among others efficiency and/amount of complex uptake in general, ability to retain the complex within the cell, i.e. to avoid leakage and of target release of the label, efficiency of uptake of a particular iron binding protein and/or targeting to particular tissues or cells and, thus suitability to treat or ameliorate a particular disease. The present inventors have, e.g. observed that CD45⁺ leukocytes, which express one or more of the following antigens: CD204, CD206, CD200R, CCR2 have a preference for ferritin uptake over the uptake of other iron binding proteins. Thus, if the iron binding protein in the complex is ferritin it is preferred to select CD45⁺ leukocytes that express one or more of the following antigens: CD204, CD206, CD200R, CCR2. Accordingly, in a preferred embodiment of the present invention

-   -   (i) the monocyte is a CD11b⁺ monocyte, preferably selected from         the group consisting of a CD11b⁺ CD14⁺ monocyte, a CD11b⁺ CD16⁺         monocyte, a CD11b⁺ CD14⁺ CD16⁺ monocyte, a CD11b⁺ CD14⁺ MHCII⁺         monocyte, a CD11b⁺ CD14⁺ CD115⁺ monocyte, CD11b⁺ CD114⁺         monocyte, CD11b⁺ CD116⁺ monocyte, CD11b⁺ CCR1⁺ monocyte, CD11b⁺         CCR2⁺ monocyte, CD11b⁺ CX3CR⁺ monocyte, CD11b⁺ CXR4⁺ monocyte,         CD11b⁺ CXR6⁺ monocyte and a CD11b⁺ CD14⁺ CD33⁺ monocyte;     -   (ii) the differentiated monocyte is selected from the group         consisting of a macrophage, an activated macrophage, preferably         a CD11b⁺ macrophage, more preferably a CD11b⁺ CD16⁺ macrophage,         CD11b⁺ CD32⁺ macrophage, CD11b⁺ CD64⁺ macrophage, CD11b⁺ CD68⁺         macrophage, preferably a CD11b⁺ CD86⁺ M1 macrophage, preferably         producing inducible nitric oxide synthetase (iNOS) and/or         secreting interleukin 12 (IL-12) or preferably CD11b⁺ CCR2⁺ M2         macrophage, CD11b⁺ CD204⁺ M2 macrophage, CD11b⁺ CD206⁺ M2         macrophage, CD11b⁺ CD204⁺ CD206⁺ M2 macrophage, CD11b⁺ Major         Histocompatibility Complex II⁺ (MHCII⁺) (low or hi expression)         M2 macrophage, CD11b⁺ CD200R⁺ M2 macrophage, CD11b⁺ CD163⁺ M2         macrophage or activated macrophage producing and/or secreting         Arginase-1 and/or interleukin 10 (IL-10); or a dendritic cell,         preferably with expression of CD11b CD11c, CD11b CD80, CD11c         CD80, CD11c CD86, CD11c MHCII and CD11c CD123, preferably the         differentiated monocyte is not a foam cell expressing         Lectin-like oxidized low-density lipoprotein receptor-1 (Lox1⁺),         C-X-C chemokine receptor type 7 (CXCR7⁺) and

Nuclear factor (erythroid-derived 2)-like 2 (NRF2⁺). A foam cell is a type of macrophage that localize to fatty deposits on blood vessel walls, where they ingest low-density lipoproteins and become loaded with lipids giving them a foamy appearance. These cells secrete various substances involved in plaque growth and their death promotes inflammation, thereby contributing to cardiovascular disease;

-   -   (iii) monocyte or activated monocyte expressing of at least one         chemokine receptor, preferably selected from the group         consisting of CCR1, CCR2, CXR4, and CXR6, or at least one growth         factor receptor, preferably selected from the group consisting         of macrophage colony stimulating factor Receptor (CD115),         granulocyte colony stimulating factor Receptor (CD114), and         granulocyte-macrophage colony stimulating factor Receptor         (consisting of CD116 and CD131); monocytes of these         characteristics are particular suitable to treat inflammatory         conditions and cancer;     -   (iv) the lymphocyte is selected from the group consisting of a         CD3⁺ and CD4⁺ or CD8⁺ T lymphocyte, or a CD19⁺, CD20⁺, CD21⁺,         CD19+CD20+, CD19+CD21+, CD20⁺ CD21+, or CD19⁺ CD20⁺ CD21⁺ B         lymphocyte; or     -   (v) the granulocyte is selected from the group consisting of a         neutrophil, preferably a CD66b⁺ neutrophil, an eosinophil and a         basophil, preferably a CD193⁺ eosinophil. In a preferred         embodiment of the targeted delivery system of the present         invention the activated macrophage:     -   (i) is producible by in vitro incubation of a monocyte or         macrophage or their precursors with a factor capable of altering         expression markers on macrophages, preferably         -   (a) with at least one M1 inducer,         -   (b) with at least one M2 inducer,         -   (c) or with a factor capable of altering the macrophages             ability to secrete cytokines, preferably IL-10 and IL-12,             chemokines and/or to produce iNOS, arginase or other             immunomodulating enzymes; examples of such factors are:             activated platelets, IL-4, IL-10, IL-13, immune complex of             an antigen and antibody, IgG, heat activated gamma-globulin,             glucocorticosteroid, tumour growth factor-β (TGF-β), IL-1R,             CC-chemokine ligand 2 (CCL-2), IL-6, Macrophage             colony-stimulating factor (M-CSF), peroxisome             proliferator-activated receptor γ (PPARγ) agonist, leukocyte             inhibitory factor (LIF), adenosine, helminth and fungal             infection, lipopolysaccharide (LPS), interferon γ (INF-γ),             granulocyte macrophage colony stimulating factor (GM-CSF)             and viral and bacterial infection; in this respect it was             observed that activation of a monocyte with a M1 inducer,             particularly LPS will cause cell to express iNOS, that             activation of a monocyte with a M1 inducer, particularly LPS             will cause cell not to express Arginase-1, that activation             of a monocyte with a M2 inducer, particularly IL-4 will             cause cell to express Arginase-1, and that activation of a             monocyte with a M2 inducer, particularly IL-4 will cause             cell not to express iNOS,     -   (ii) is characterized by expression of at least one of following         antigens: CD64, CD86, CD16, CD32, high expression of MHCII,         and/or production of iNOS and/or IL-12;     -   (iii) is producible by in vitro incubation of a monocyte or         macrophage with a factor capable of inducing the ability of the         macrophage to phagocytose, e.g. IL-18, opsonins (for example         complement-derived proteins such as iC3b, immunoglobulin G),         calcitonin gene-related peptide (CGRP), lipopolysaccharide         (LPS), interferon γ (INF-γ), granulocyte macrophage colony         stimulating factor (GM-CSF), viral infection and/or bacterial         infection;     -   (iv) is characterized by expression of at least one of following         antigens: CD204, CD206, CD200R; CCR2, transferrin receptor         (TfR), CXC-motive chemokine receptor 4 (CXCR4), CD163, and/or T         cell immunoglobulin-domain and mucin-domain 2 (TIM-2), and/or         show low expression of MHCII; activated macrophages having these         properties are particularly suitable for complexes comprising         ferritin as the iron binding protein;     -   (v) has the ability to phagocytose; and/or     -   (vi) is capable of cytokine secretion, preferably of IL-12, or         IL-10, or production of inducible nitric oxide synthetase (iNOS)         (or other pro-inflammatory compounds), arginase or other         immunosuppressive/anti-inflammatory compounds.

In a preferred embodiment of the targeted delivery system of the present invention the M1 inducer for differentiating macrophages into M1 macrophages is selected from the group consisting of lipopolysaccharide (LPS), interferon γ (INF-γ), granulocyte macrophage colony stimulating factor (GM-CSF) and viral and bacterial infection and the M2 inducer for differentiating macrophages into M2 macrophages is selected from the group consisting of IL-4, IL-10, IL-13, immune complex of an antigen and antibody, IgG, heat activated gamma-globulin, glucocorticosteroid, tumour growth factor-β (TGF-β), IL-1R, CC-chemokine ligand 2 (CCL-2), IL-6, Macrophage colony-stimulating factor (M-CSF), peroxisome proliferator-activated receptor γ (PPARγ) agonist, leukocyte inhibitory factor (LIF), adenosine, helminth and fungal infection.

It has been surprisingly found by the present inventors that both complex loaded M1 macrophages and M2 macrophages are suitable for targeted active agent delivery into hypoxic tissues, preferably a tumour or its metastasis. In general we observed that 3 to 5% of the administered M1 macrophages localized at the tumour site while about 35% of the M2 macrophages showed tumour specific targeting. However, this general advantage of M2 macrophages were offset when using a complex comprising haemoglobin and label, since significantly larger amounts of this complex could be loaded into M1 macrophages than into M2 macrophages. Generally this specific tropisms makes M2 macrophages more suitable for treating tumour and diseases characterized by hypoxic tissue.

In a preferred embodiment of the targeted delivery system of the present invention the monocyte:

-   -   (i) is producible from a CD34⁺ hematopoietic precursor cell;     -   (ii) is producible by in vitro incubation of monocytes with at         least one inducer, preferably M1 or M2 inducer, more preferably         at least one M2 inducer;     -   (iii) is characterized by expression of at least one of the         following antigens: TfR, CD163, TIM-2, CD14, CD16, CD33, and/or         CD115;     -   (iv) is characterized by expression of at least one of the         following antigens: TfR, CD163, TIM-2, CXCR4, CD14, and/or CD16;         and/or     -   (v) has the ability to phagocytose.

In this embodiment of the targeted delivery system of the present invention the M1 inducer for differentiating monocytes is selected from the group consisting of LPS, INF-γ, GM-CSF or viral or bacterial infection or the M2 inducer for differentiating monocytes is selected from the group consisting of IL-4, IL-10, IL-13, immune complex of an antigen and antibody, IgG, heat activated gamma-globulins, Glucocorticosteroids, TGF-β, IL-1R, CCL-2, IL-6, M-CSF, PPARγ agonist, Leukocyte inhibitory factor (LIF), cancer-conditioned medium, cancer cells, adenosine and helminth or fungal infection.

It has been surprisingly found by the present inventors that monocytes are suitable for targeted active agent delivery into hypoxic tissues, preferably the tumour or its metastasis while monocytes treated with M2 activators are more suitable for targeted active agent delivery into hypoxic tissues, preferably the tumour or its metastasis. This specific tropisms make monocytes treated with M2 activators more suitable to targeting tumour and hypoxic sites.

In a preferred embodiment of the targeted delivery system of the present invention the lymphocyte:

-   -   (i) is obtainable from blood, spleen, or bone marrow or is         producible from a CD34⁺ precursor cell as known to the skilled         person and also described in the, e.g. Lefort and Kim, 2010, J         Vis Exp 40: 2017; Tassone and Fidler, 2012, Methods in Molecular         Biology 882: 351-357; Kouro et al. 2005, Current Protocols in         Immunology, 66:F22F.1:22F.1.1-22F.1.9.;     -   (ii) is an immunologically competent lymphocyte;     -   (iii) expresses antigen specific T cell receptors; and/or     -   (iv) is characterized by expression of at least one of the         following antigens: (a) CD3 and CD4 or CD8 or (b): CD19, CD20,         CD21, CD19 CD20, CD19 CD21, CD20 CD21, or CD19 CD20 CD21         antigen, and is preferably capable of producing immunoglobulins.

In a preferred embodiment of the targeted delivery system of the present invention the granulocyte:

-   -   (i) is obtainable from blood, spleen or bone marrow or         producible from a CD34⁺ precursor cell as described, e.g. in         Kuhs et al. 2015, Curr Protoc Immunol 111:7.23-1-7.23.16;         Coquery et al. 2012, Cytometry A 81(9): 806-814; Swemydas and         Lionakis 2013, J Vis Exp 77: 50586.;     -   (ii) is characterized by expression of at least one of the         following CD66b and/or CD193;     -   (iii) is a polymorphonuclear leukocyte characterized by the         presence of granules in its cytoplasm; and/or     -   (iii) is characterized by expression of at least one of the         following: TfR, CD163, TIM-2, and/or CXCR4.

In a preferred embodiment of the targeted delivery system of the present invention the iron binding protein is selected from the group consisting of ferritin, preferably heavy (H) type ferritin, light (L) ferritin and/or mitochondrial ferritin; haemoglobin, preferably haemoglobin A, haemoglobin AS, haemoglobin SC, haemoglobin C, haemoglobin D, haemoglobin E, haemoglobin F, haemoglobin H; haemoglobin-haptoglobin complex, haemopexin, transferrin; and lactoferrin. The terms ferritin; haemoglobin, preferably haemoglobin A, haemoglobin AS, haemoglobin SC, haemoglobin C, haemoglobin D, haemoglobin E, haemoglobin F, haemoglobin H; haemoglobin-haptoglobin complex, hemopexin, transferrin; and lactoferrin encompass structural variants of the naturally occurring proteins and, thus relates to proteins that have at least 70%, preferably at least 75%, more preferably at least 80%, more preferably at least 85%, more preferably at least 90%, more preferably at least 95% more preferably at least 100% of the ability of the respective wild-type protein to bind iron ion(s). The iron binding proteins used in the context of the present invention are preferably of mammalian, more preferably mouse, rat, dog, ape, in particular, chimpanzee, or human, most preferably of human origin. Consensus sequences of the preferred iron binding proteins used in the context of the present invention are shown in FIG. 1 below. Preferred structural variants are based on the sequences indicated in FIG. 1. The residues marked with X vary among different mammalian ferritins, transferrins, and haemoglobins. The alteration of these residues is not crucial for the ability of the proteins to bind to iron ions. Accordingly, it is preferred that amino acid mutations or deletions effect one or more of the residues marked with an X.

Plasma proteins have always been privileged carriers for the delivery of active pharma ingredients in cancer therapy. Thus, albumin, the most abundant plasma protein, is currently used in therapeutic protocols for the delivery of taxane molecules and doxorubicin derivatives (Larsen M T et al. 2016, Mol Cell Ther 27;4:3).

Human transferrin and ferritin proteins have been considered as effective carriers for the delivery of small molecules to specifically target cancer cells. To date, in spite of considerable efforts, no successful transferrin or ferritin complexes have however reached the clinic (Luck A N et al. 2013, Adv Drug Deliv Rev 65(8):1012-9).

Ferritin has a cage architecture and capability of iron-binding which could be used to encapsulate labels inside its cavity. Ferritins are not abundant in plasma, but can be readily produced in high yield as recombinant proteins in common protein expression vectors such as

Escherichia coli cells. Ferritins H- or L-chains are encoded as small protein monomer (21 kDa and 19 KDa for H and L chains, respectively) capable of a 24-mer assembly into a cage-like structure, delimiting a 8 nm diameter cavity. The present inventors noted in the context of working on the present invention that H-ferritin homopolymers, represent a preferred protein construct in order to specifically deliver encapsulated drugs to CD45⁺ leukocyte cells expressing TfR. Furthermore H-ferritin targets complexed labels to the cell nucleus (and therefore directly delivers DNA-binding proteins into the nucleus.

Purified transferrin can be efficiently conjugated to various molecules through covalent linkers that are appropriately released inside the cells (Beyer U et al. 1998, J Med Chem 41(15):2701-2708). In case of transferrin, only lysine groups on the protein surface are ready available for covalent attachment.

Haemoglobin has been considered in the past as a carrier, due to its versatility in chemical conjugation with various molecules, its abundance and relative stability in the blood (Somatogen, 1993, WO1993008842 A1). Nevertheless, the lack of receptor targeting properties did not foster biomedical applications other than blood substitutes or antisickling agent. As a matter of fact, Hb can only be recognized by CD163 (haptoglobin/haemoglobin receptor) epitopes on the leukocytes, especially monocyte-macrophage origin. The CD45⁺ leukocyte, in particular macrophage based protein delivery, described in this application moved haemoglobin center stage as a target specific carrier of labels. Haemoglobin can be readily covalently linked to appropriate labels, host hydrophobic label molecules within the heme binding pocket, by exchanging heme free fluorescent porphyrines or porphyrins coupled to radiolabel or even transport small molecules combined with label linked to the heme iron. Hb can be easily modified by selective attachment of the appropriate label conjugate to the beta93 cysteine residue, the only titratable cystein on the protein surface.

Maleimido functionalized labels, are examples of labels that can be readily and specifically attached to the relevant cys beta93 residue. Alternatively, lysine residues on the Hb surface (at least 10 titratable lysine residues per Hb tetramer) may be easily amenable to label conjugation through cleavable succinimide linkers. Haemoglobin also offers a unique capability of releasing non covalently bound heme group at acidic pH values. Apo-haemoglobin thus obtained is capable of hosting several hydrophobic molecules within the empty heme pocket endowed with notable fluorescence properties (e.g. chlorine e6, hyperycin, phtalocyanine derivatives) (Dong J et al. J Photochem Photobiol B 2014, 140:163-172).

Whatever the conjugation/adsorption/binding method, haemoglobin (Hb), transferrin

(Tf) and ferritins were shown by the present inventions to be privileged carriers of labels, once loaded into appropriate cell systems with tumour targeting properties, e.g. activated macrophages. The easy, fast, cheap and safe purification procedure of these protein also provide a tremendous added value.

Based on sequences of mammalian H-type ferritins, L-type ferritins, haemoglobin alpha chains, haemoglobin beta chains and transferrins a consensus sequence was determined for each of these proteins. These are shown in FIG. 1 in SEQ ID NO: 2, 7, 9, 14, 16, 20, and 25, respectively). On this basis but also on the basis of deletion and structural analysis disclosed in the prior art a minimal fragment was determined for H-type ferritins, L-type ferritins, haemoglobin alpha chains, and haemoglobin beta chains sufficient for uptake by CD45⁺ leukocytes. These are shown in SEQ ID NO: 1, 3, 5 (H-type ferritin); 8, 10, 12 (L-type ferritin), 15 and 17 (haemoglobin alpha chain) and 19 and 21 (haemoglobin beta chain. Transferrin comprises a N-terminally located domain and a C-terminally located domain that are necessary for binding iron and uptake by CD45⁺ leukocytes, if comprised in one polypeptide and positioned between 100 to 450 amino acids apart, preferably between 150 to 400, more preferably between 200 to 350 amino acids and more preferably 250 to 320 amino acids apart. The N-terminal domain comprises amino acids 1 to 82 of full length consensus transferrin (SEQ ID NO: 25) or full length human transferrin (SEQ ID NO: 28). The C-terminal domain comprises amino acids 396 to 510 of full length consensus transferrin (SEQ ID NO: 25) or full length human transferrin (SEQ ID NO: 28). In each case an X is indicated in the consensus sequence it independently stands for any amino acid and characterizes an amino acid not or only poorly conserved among mammalian H-type ferritins, which can be mutated without or little detriment to the iron binding properties of the respective iron binding protein. It is preferred that X in each case takes on the meaning of the amino acid of the respective human iron binding protein aligning with X. This information can be taken, e.g. from FIG. 1, which shows alignments of the consensus sequences with human an in some instances mouse proteins.

Preferred H-type ferritins comprise or consist of the amino acid sequence indicated in SEQ ID NO: 1 and variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a H-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 1 to be taken up by CD45⁺ leukocytes, preferably M2 leukocytes. Within SEQ ID NO: 1 X at position 5 may be present or absent, if present it means any amino acid, preferably Ile, X at position 6 means any amino acid, preferably Asn, X at position 14 means any amino acid, preferably Tyr, X at position 24 means any amino acid, preferably Tyr or Cys, X at position 66 means any amino acid, preferably Phe, X at position 68 means any amino acid, preferably Gln, X at position 75 means any amino acid, preferably Arg or Cys, X at position 90 means any amino acid, preferably His, X at position 94 means any amino acid, preferably Ser or Asn, X at position 120 may be present or absent, if present it means any amino acid, preferably His or Tyr, more preferably His, X at position 123 means any amino acid, preferably Asn or Ser, more preferably Asn, X at position 128 means any amino acid, preferably Ala or Ser, more preferably Ala.

In a preferred embodiment the H-type ferritin comprises or consists of murine ferritin according to SEQ ID NO: 3. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a H-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 3 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the H-type ferritin comprises or consists of human ferritin according to SEQ ID NO: 5. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a H-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 5 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the H-type ferritin comprises or consists of a mammalian consensus sequence derived from aligning full length H-type ferritins according to SEQ ID NO: 2 or 7, with 2 being preferred. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a H-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 2 or 7, with 2 being preferred to be taken up by CD45⁺ leukocytes, preferably M2 macrophages. In SEQ ID NO: 2 X at position 6 can be any naturally occurring amino acid, preferably Pro, X at position 14 can be any naturally occurring amino acid, preferably His, X at position 16 can be any naturally occurring amino acid, preferably Asp, X at position 21 may be present or absent, if present it means any amino acid, preferably Ile, X at position 22 means any amino acid, preferably Asn, X at position 30 can be any naturally occurring amino acid, preferably Tyr, X at position 40 can be any naturally occurring amino acid, preferably Tyr or Cys, more preferably Tyr, X at position 82 can be any naturally occurring amino acid, preferably Phe, X at position 84 can be any naturally occurring amino acid, preferably Gln, X at position 91 can be any naturally occurring amino acid, preferably Arg or Cys, more preferably Cys, X at position 106 can be any naturally occurring amino acid, preferably His, X at position 110 can be any naturally occurring amino acid, preferably Asn or Ser, more preferably Asn, X at position 137 can be any naturally occurring amino acid, preferably His or Tyr, more preferably His, X at position 140 can be any naturally occurring amino acid, preferably Asn or Ser, more preferably Asn, X at position 145 can be any naturally occurring amino acid, preferably Ala or Ser, more preferably Ala, X at position 164 can be any naturally occurring amino acid, preferably Ala or Ser, more preferably Ser, X at position 166 can be any naturally occurring amino acid, preferably Met or Leu, preferably Leu, X at position 178 can be any naturally occurring amino acid, preferably Asp or His, more preferably Asp, X at position 181 is absent or any naturally occurring amino acid, preferably Asn, X at position 182 is absent or any naturally occurring amino acid, preferably Glu, X at position 183 is absent or any naturally occurring amino acid, preferably Ser. In SEQ ID NO: 7 X at position 6 can be any naturally occurring amino acid, preferably Pro X at position 14 can be any naturally occurring amino acid, preferably His, X at position 16 can be any naturally occurring amino acid, preferably Asp, X at position 21 may be present or absent, if present it means any amino acid, preferably Ile, X at position 29 can be any naturally occurring amino acid, preferably Tyr, X at position 81 can be any naturally occurring amino acid, preferably Phe, X at position 83 can be any naturally occurring amino acid, preferably Gln, X at position 105 can be any naturally occurring amino acid, preferably His, X at position 144 can be any naturally occurring amino acid, preferably Ala or Ser, more preferably Ala, X at position 180 is absent or any naturally occurring amino acid, preferably Asn, X at position 181 is absent or any naturally occurring amino acid, preferably Glu, X at position 182 is absent or any naturally occurring amino acid, preferably Ser.

In a preferred embodiment the H-type ferritin comprises or consists of murine full length ferritin according to SEQ ID NO: 4 being preferred. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a murine H-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 4 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the H-type ferritin comprises or consists of human full length ferritin according to SEQ ID NO: 6 being preferred. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a human H-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 6 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

Preferred L-type ferritins comprise or consist of the amino acid sequence indicated in SEQ ID NO: 8 and variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a L-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 8 to be taken up by CD45⁺ leukocytes, preferably M2 leukocytes. In SEQ ID NO: 8 X at position at position 5 can be any naturally occurring amino acid, preferably Asp or Glu, more preferably Asp, X at position 12 can be any naturally occurring amino acid, preferably Arg or Ser, more preferably Ser, X at position 17 can be any naturally occurring amino acid, preferably Ser or Arg, more preferably Ser, X at position 19 can be any naturally occurring amino acid, preferably Arg or Gln, more preferably Gln, X at position 29 can be any naturally occurring amino acid, preferably Phe, X at position 30 can be any naturally occurring amino acid, preferably Tyr or Phe, more preferably Tyr, X at position 42 can be any naturally occurring amino acid, preferably Ser or Gly, more preferably Ser, X at position 56 can be any naturally occurring amino acid, preferably Ala or Tyr, more preferably Tyr, X at position 61 can be any naturally occurring amino acid, preferably Glu or Lys, more preferably Lys, X at position 62 can be any naturally occurring amino acid, preferably Met or Phe, more preferably Met, X at position 65 can be any naturally occurring amino acid, preferably Asp or Gln, more preferably Gln, X at position 75 can be any naturally occurring amino acid, preferably Ile or Val, more preferably Ile, X at position 76 can be any naturally occurring amino acid, preferably Lys or Gln, more preferably Lys, X at position 79 can be any naturally occurring amino acid, preferably Ala or Ser, more preferably Ala, X at position 80 can be any naturally occurring amino acid, preferably Glu or Gln, more preferably Gln, X at position 87 can be any naturally occurring amino acid, preferably Pro or Gln, more preferably Pro, X at position 88 can be any naturally occurring amino acid, preferably Glu or Asp, more preferably Asp, X at position 91 can be any naturally occurring amino acid, preferably Glu or Lys, more preferably Lys, X at position 94 can be any naturally occurring amino acid, preferably Met or Leu, more preferably Leu, X at position 96 can be any naturally occurring amino acid, preferably Met or Leu, more preferably Met, X at position 99 can be any naturally occurring amino acid, preferably Lys or Asn, preferably Lys, X at position 115 can be any naturally occurring amino acid, preferably Thr or Ala, more preferably Thr, X at position 119 can be any naturally occurring amino acid, preferably Leu, X at position 125 can be any naturally occurring amino acid, preferably Ser or Thr, more preferably Thr, X at position 127 can be any naturally occurring amino acid, preferably Tyr or Phe, more preferably Phe, X at position 130 can be any naturally occurring amino acid, preferably Lys or Glu, more preferably Glu,

X at position 140 can be any naturally occurring amino acid, preferably Asp or Asn, more preferably Asp, X at position 146 can be any naturally occurring amino acid, preferably Arg or His, more preferably His, and X at position 148 can be any naturally occurring amino acid, preferably Leu or Val, more preferably Leu.

In a preferred embodiment the L-type ferritin comprises or consists of murine L-type ferritin according to SEQ ID NO: 10. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a L-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 10 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the L-type ferritin comprises or consists of human ferritin according to SEQ ID NO: 12. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a L-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 12 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the L-type ferritin comprises or consists of a mammalian consensus sequence derived from aligning full length H-type ferritins according to SEQ ID NO: 9 or 14, with 9 being preferred. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a L-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 9 or 14, with 9 being preferred to be taken up by CD45⁺ leukocytes, preferably M2 macrophages. In SEQ ID NO: 9 X at position 12 X at position 12 can be any naturally occurring amino acid, preferably Asp or Glu, more preferably Asp, X at position 19 can be any naturally occurring amino acid, preferably Ser or Arg, more preferably Ser, X at position 24 can be any naturally occurring amino acid, preferably Ser or Arg, more preferably Ser, X at position 26 can be any naturally occurring amino acid, preferably Arg or Gln, more preferably Gln, X at position 36 can be any naturally occurring amino acid, preferably Phe, X at position 37 can be any naturally occurring amino acid, preferably Tyr or Phe, more preferably Tyr, X at position 47 can be any naturally occurring amino acid, preferably Ser or Gly, more preferably Ser, X at position 63 can be any naturally occurring amino acid, preferably Ala or Tyr, more preferably Tyr, X at position 68 can be any naturally occurring amino acid, preferably Glu or Lys, more preferably Lys, X at position 69 can be any naturally occurring amino acid, preferably Met or Phe, more preferably Met, X at position 72 can be any naturally occurring amino acid, preferably Asp or Gln, more preferably Gln, X at position 82 can be any naturally occurring amino acid, preferably Ile or Val, more preferably Ile, X at position 83 can be any naturally occurring amino acid, preferably Lys or Gln, more preferably Lys, X at position 86 can be any naturally occurring amino acid, preferably Ala or Ser, more preferably Ala, X at position 87 can be any naturally occurring amino acid, preferably Glu or Gln, more preferably Gln, X at position 94 can be any naturally occurring amino acid, preferably Pro or Gln, more preferably Pro, X at position 95 can be any naturally occurring amino acid, preferably Glu or Asp, more preferably Asp, X at position 98 can be any naturally occurring amino acid, preferably Glu or Lys, more preferably Lys, X at position 101 can be any naturally occurring amino acid, preferably Met or Leu, more preferably Leu, X at position 103 can be any naturally occurring amino acid, preferably Met or Leu, more preferably Met, X at position 106 can be any naturally occurring amino acid, preferably Lys or Asn, preferably Lys, X can be any naturally occurring amino acid, X at position 126 can be any naturally occurring amino acid, preferably Leu, X at position 132 can be any naturally occurring amino acid, preferably Ser or Thr, more preferably Thr, X at position 134 can be any naturally occurring amino acid, preferably Tyr or Phe, more preferably Phe, X at position 137 can be any naturally occurring amino acid, preferably Lys or Glu, more preferably Glu, X at position 147 can be any naturally occurring amino acid, preferably Asp or Asn, more preferably Asp, X at position 153 can be any naturally occurring amino acid, preferably Arg or His, more preferably His, X at position 155 can be any naturally occurring amino acid, preferably Leu or Val, more preferably Leu, X at position 161 can be absent or any naturally occurring amino acid, preferably Ala, X at position 163 can be absent or any naturally occurring amino acid, preferably Thr, X at position 166 can be absent or any naturally occurring amino acid, preferably Pro, and X at position 168 can be any naturally occurring amino acid, preferably Gly or Ala, more preferably Ala. In SEQ ID NO: 14 X at position 36 can be any naturally occurring amino acid, preferably Phe, X at position 37 can be any naturally occurring amino acid, preferably Tyr or Phe, more preferably Tyr, X at position 94 can be any naturally occurring amino acid, preferably Pro or Gln, more preferably Pro, X at position 126 can be any naturally occurring amino acid, preferably Leu, X at position 137 can be any naturally occurring amino acid, preferably Lys or Glu, more preferably Glu, X at position 147 can be any naturally occurring amino acid, preferably Asp or Asn, more preferably Asp, X can be any naturally occurring amino acid, X at position 163 can be absent or any naturally occurring amino acid, preferably Thr, X at position 166 can be absent or any naturally occurring amino acid, preferably Pro, X at position 168 can be any naturally occurring amino acid, preferably Gly or Ala, more preferably Ala.

In a preferred embodiment the L-type ferritin comprises or consists of murine full length ferritin according to SEQ ID NO: 11 being preferred. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a murine L-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 11 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the L-type ferritin comprises or consists of human full length ferritin according to SEQ ID NO: 13 being preferred. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a human L-type ferritin consisting of the amino acid sequence according to SEQ ID NO: 13 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the alpha haemoglobin comprises or consists of a minimal mammalian consensus sequence derived from aligning full length alpha haemoglobins according to SEQ ID NO: 15 Preferred comprise or consist of the amino acid sequence indicated in SEQ ID NO: 15 and variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of an alpha haemoglobin consisting of the amino acid sequence according to SEQ ID NO: 15 to be taken up by CD45⁺ leukocytes, preferably M1 macrophages.

In a preferred embodiment the alpha haemoglobin comprises or consists of a minimal human amino acid sequence derived of human alpha haemoglobin according to SEQ ID NO: 17. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of an alpha haemoglobin consisting of the amino acid sequence according to SEQ ID NO: 17 to be taken up by CD45⁺ leukocytes, preferably M1 macrophages.

In a preferred embodiment the alpha haemoglobin comprises or consists of a mammalian consensus sequence derived from aligning full length alpha haemoglobins according to SEQ ID NO: 16. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of an alpha haemoglobins consisting of the amino acid sequence according to SEQ ID NO: 16 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the alpha haemoglobin comprises or consists of human full length alpha haemoglobin according to SEQ ID NO: 18. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a human full length alpha haemoglobin consisting of the amino acid sequence according to SEQ ID NO: 18 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the alpha haemoglobin comprises or consists of a minimal mammalian consensus sequence derived from aligning full length beta haemoglobins according to SEQ ID NO: 19 and variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a beta haemoglobin consisting of the amino acid sequence according to SEQ ID NO: 19 to be taken up by CD45⁺ leukocytes, preferably M1 macrophages.

In a preferred embodiment the alpha haemoglobin comprises or consists of a minimal human amino acid sequence derived of human beta haemoglobin according to SEQ ID NO: 21. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a beta haemoglobin consisting of the amino acid sequence according to SEQ ID NO: 21 to be taken up by CD45⁺ leukocytes, preferably M1 macrophages.

In a preferred embodiment the beta haemoglobin comprises or consists of a mammalian consensus sequence derived from aligning full length beta haemoglobins according to SEQ ID NO: 20. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of an beta haemoglobins consisting of the amino acid sequence according to SEQ ID NO: 20 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the beta haemoglobin comprises or consists of human full length beta haemoglobin according to SEQ ID NO: 22. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a human full length beta haemoglobin consisting of the amino acid sequence according to SEQ ID NO: 22 to be taken up by CD45⁺ leukocytes, preferably M2 macrophages.

In a preferred embodiment the transferrin comprises or consists of a mammalian consensus sequence derived from aligning full length alpha haemoglobins according to SEQ ID NO: 25. Thus, particularly, preferred transferrins comprise or consist of the amino acid sequence indicated in SEQ ID NO: 25 and of variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a transferrin consisting of the amino acid sequence according to SEQ ID NO: 25 to be taken up by CD45⁺ leukocytes preferably M1 macrophages.

In a preferred embodiment the transferrin comprises or consists of human transferrin according to SEQ ID NO: 28. Accordingly, preferred structural variants have at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a transferrin consisting of the amino acid sequence according to SEQ ID NO: 28 to be taken up by CD45⁺ leukocytes, preferably M1 macrophages.

The iron binding properties of transferrins are dependent on a N-terminally and C-terminally located domain. Thus, in a preferred embodiment the transferrin used in the present invention comprises at least the N-terminal domain according to SEQ ID NO: 23 and the C-terminal domain according to SEQ ID NO: 24. Preferred transferrin comprise proteins that comprise the amino acid sequence indicated in SEQ ID NO: 23 and 24 as well as variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a transferrin consisting of the amino acid sequence according to SEQ ID NO: 23 and 24 to be taken up by CD45⁺ leukocytes, preferably Ml macrophages. SEQ ID NO: 23 or 24 indicates a consensus sequence of mammalian transferrins.

Thus, in a preferred embodiment the transferrin used in the present invention comprises at least the N-terminal domain according to SEQ ID NO: 26 and the C-terminal domain according to SEQ ID NO: 27. Preferred transferrin comprise proteins that comprise the amino acid sequence indicated in SEQ ID NO: 26 and 27 as well as variants thereof having at least 70% amino acid identity, more preferably at least 75% amino acid identity, more preferably at least 80% amino acid identity, more preferably at least 85% amino acid identity, more preferably at least 90% amino acid identity, more preferably at least 95% amino acid identity and in each case at least 70% of the ability of a transferrin consisting of the amino acid sequence according to SEQ ID NO: 26 and 27, respectively, to be taken up by CD45⁺ leukocytes, preferably M1 macrophages.

Preferred ferritins, also comprise proteins that, irrespective of the given amino acid sequence, conform to the 24-mer subunit assembly of a four helix bundle protein module, falling within given sequence alignments of distantly related proteins as defined by 3D structure based alignments.

It is a surprising observation of the present inventors that monocytes, macrophages and preferably M2 macrophages are able to uptake the amount of label enough to make them visible using imaging methods at the site of their accumulation (e.g. in the tumour or its metastasis, hypoxia site). Surprisingly, inventors found out that lymphocytes and M2 macrophages are better in uptake of complexes comprising one or more ferritin and one or more label, that M1 macrophages are better in uptake of complexes comprising one or more haemoglobin and one or more label and that macrophages are better in uptake of complexes comprising one or more transferrin and one or more label. Accordingly, based on the tissue and cellular tropism of CD45⁺ leukocytes: monocytes, M1 and M2 macrophages, granulocytes and lymphocytes, described above complexes comprising one or more ferritin and one or more label are used to load M2 macrophages, lymphocytes or monocytes, if the tropism of M2 macrophages, lymphocytes or monocytes is desired and complexes comprising one or more haemoglobin and one or more label are used to load M1 macrophages, if the tropism of M1 macrophages is desired.

In a preferred embodiment of the targeted delivery system of the present invention the label is selected from a fluorescent dye, a fluorescence emitting isotope, a radioisotope, a detectable polypeptide or nucleic acid encoding such a detectable polypeptide and a contrast agent.

In a preferred embodiment of the targeted delivery system of the present invention the label comprises a chelating agent which forms a complex with divalent or trivalent metal cations.

In a preferred embodiment of the targeted delivery system of the present invention the chelating agent is selected from the group consisting of 1,4,7,10-tetraazacyclododecane-N,N′,N,N′-tetraacetic acid (DOTA), ethylenediaminetetraacetic acid (EDTA), 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), triethylenetetramine (TETA), iminodiacetic acid, Diethylenetriamine-N,N,N′,N′,N″-pentaacetic acid (DTPA) and 6-Hydrazinopyridine-3-carboxylic acid (HYNIC).

In a preferred embodiment of the targeted delivery system of the present invention the contrast agent comprises a paramagnetic agent, preferably selected from Gd, Eu, W and Mn, or ferrihydride.

In a preferred embodiment of the targeted delivery system of the present invention the radioisotope/fluorescence emitting isotope is selected from the group consisting of alpha radiation emitting isotopes, gamma radiation emitting isotopes, Auger electron emitting isotopes, X-ray emitting isotopes, fluorescence emitting isotopes, such as ¹⁸F, ⁵¹Cr, fluorescent ⁶⁵Tb, ⁶⁷Ga, ⁶⁸Ga, ¹¹¹In, ^(99m)Tc, ¹⁴⁰La, ¹⁷⁵Yb, ¹⁵³Sm, ¹⁶⁶Ho, ⁸⁸Y, ⁹⁰Y, ¹⁴⁹Pm, ¹⁷⁷Lu, ⁴⁷Sc, ¹⁴²Pr, ¹⁵⁹Gd, ²¹²Bi, ⁷²As, ⁷²Se, ⁹⁷Ru, ¹⁰⁹Pd, ¹⁰⁵Rh, ^(101m15)Rh, ¹¹⁹Sb, ¹²⁸Ba, ¹²³I, ¹²⁴I, ¹³¹I, ¹⁹⁷Hg, ²¹¹At, ¹⁶⁹Eu, ²⁰³Pb, ²¹²Pb, ⁶⁴Cu, ⁸⁹Zr, ⁶⁷Cu, ¹⁸⁸Re, ¹⁸⁶Re, ¹⁹⁸Au and ¹⁹⁹Ag as well as conjugates and combinations of above with proteins, peptides, small molecular inhibitors, antibodies or other compounds (e.g. ¹⁸F-FDG or ⁶⁴Cu-porfirin).

In a preferred embodiment of the targeted delivery system of the present invention the fluorescence dye is selected from the group consisting of the following classes of fluorescent dyes: Xanthens, Acridines, Oxazines, Cynines, Styryl dyes, Coumarines, Porphines, Metal-Ligand-Complexes, Fluorescent proteins, Nanocrystals, Perylenes and Phtalocyanines as well as conjugates and combinations of these classes of dyes.

In a preferred embodiment of the targeted delivery system of the present invention the detectable polypeptide is an autofluorescent protein, preferably green fluorescent protein or any structural variant thereof with an altered adsorption and/or emission spectrum.

As has been outlined above, the targeted delivery system of the present invention has particular suitability to deliver labels to hypoxic areas.

In a preferred embodiment of the isolated targeted delivery system of the present invention the bond(s) between the iron binding protein(s) and the label comprised in the complex are covalent and/or non-covalent; and/or the label comprised in the complex is entrapped/encapsulated by the iron binding protein, preferably ferritin or multimers thereof. In one embodiment the covalent and/or non-covalent coupling is indirect through a linker or spacer. If the formation of covalent bonds is desired, relevant thiol, amino or carboxyl groups of the iron binding proteins are used to covalently couple labels directly or indirectly to the one or more iron binding protein. It is also envisioned that different labels are comprised in the complex. For example, one type of label may be bound to an iron binding protein (non-covalently bound), while another type of label is encapsulated. This approach utilizes different release rates of the labels from the iron binding protein once delivered to the targeted tissue and/or cells.

In a third aspect the present invention relates to a method of preparation of the isolated targeted delivery system of the present invention comprising the steps of

-   -   a) providing purified iron binding protein as defined above;     -   b) covalently or non-covalently linking a label to and/or         encapsulating a label in an iron binding protein;     -   c) providing a CD45+ leukocyte cell as defined above; and     -   d1) incubating the CD45+ leukocyte cell in the presence of the         complex of the iron binding protein and the label produced in         step b) until the CD45+leukocyte cell is at least partially,         preferably fully loaded with the complex of the iron binding         protein and the label produced in step b); and/or     -   d2) incubating CD45⁺ leukocyte cell in the presence of the label         until the CD45⁺ leukocyte cell is at least partially labelled         with the label.

In a further aspect the present invention relates to the isolated targeted delivery system producible by the method according to the second aspect of the present invention.

The formation of the adduct between the protein and the label may be a non-covalent label binding to the target protein and can be described as follows: In the case of ferritin, labels can be typically encapsulated within the internal cavity (physical confinement) by exploiting the association dissociation properties of the ferritin macromolecule itself. Label molecules are held in place by non-covalent interactions with amino acid residues within the cavity internal surface. Haemoglobin macromolecules also offer the possibility of non-covalent binding of selected labels molecules that may be hosted within the heme binding pocket of haemoglobin itself. The heme can be displaced by the pocket and be replaced by labels with appropriate hydrophobicity profile. In a further aspect, all proteins considered in the present invention may be covalently attached to labels modified by specific active linker moieties reactive towards thiol or amino groups of the protein itself. As such, ferritins or haemoglobin may be linked to cysteine thiol reactive labels bearing a peptide based cleavable linker (e.g. cathepsin sensitive valine-citrulline sequence and para-aminobenzylcarbamate spacer). The peptide-based linker binds the protein to the label in a stable manner so the label is not easily released from the protein under physiologic conditions and help prevent toxicity and/or leakage to healthy cells and ensure specificity of the labeling. The protein label adduct thus generated is capable of attaching to the selected receptor types, i.e. CD163 for haemoglobin and TfR for ferritin or transferrin, respectively. Once bound the protein label adduct is internalised by endocytosis and thus selectively taken up by targeted cells. The vesicle containing the label is fused with lysosomes and lysosomal cysteine proteases, particularly cathepsin B start to break down valine-citrulline linker and the label is no longer bound to the antibody and is released directly into the tumour environment.

Alternatively, a label bearing a linker that specifically bind to lysine residues generating a covalent complex with ferritin, haemoglobin or transferrin in a reaction is used.

The term “full load” is used in the context of the present invention to refer to the maximum amount of iron binding protein, preferably ferritin, complexed with a label that can be taken up by the CD45+ leukocyte cell, preferably macrophage more preferably activated macrophage.

In a fourth aspect the present invention relates to the isolated targeted delivery system of the first aspect of the present invention or producible according to the method of the second aspect of the invention for use as a diagnostic.

In a fifth aspect the present invention relates to a diagnostic composition comprising the isolated targeted delivery system of the first aspect of the present invention or producible according to the method of the second aspect of the invention and a pharmaceutically acceptable carrier and/or suitable excipient(s). Since the isolated targeted delivery system comprises living cells, it is preferred that carriers and excipients are chosen in such to keep the cells alive.

“Pharmaceutically acceptable” means approved by a regulatory agency of the Federal or a state government or listed in the U.S. Pharmacopeia or other generally recognized pharmacopeia for use in animals, and more particularly in humans.

The term “carrier”, as used herein, refers to a pharmacologically inactive substance such as but not limited to a diluent, excipient, surfactants, stabilizers, physiological buffer solutions or vehicles with which the label is administered. Such pharmaceutical carriers can be liquid or solid. Liquid carrier include but are not limited to sterile liquids, such as saline solutions in water and oils, including but not limited to those of petroleum, animal, vegetable or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil and the like. Saline solutions and aqueous dextrose and glycerol solutions can also be employed as liquid carriers, particularly for injectable solutions. A saline solution is a preferred carrier when the pharmaceutical composition is administered intravenously. Examples of suitable pharmaceutical carriers are described in “Remington's Pharmaceutical Sciences” by E. W. Martin.

Suitable pharmaceutical “excipients” include starch, glucose, lactose, sucrose, gelatine, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, dried skim milk, glycerol, propylene, glycol, water, ethanol and the like.

“Surfactants” include anionic, cationic, and non-ionic surfactants such as but not limited to sodium deoxycholate, sodium dodecylsulfate, Triton X-100, and polysorbates such as polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 65 and polysorbate 80.

“Stabilizers” include but are not limited to mannitol, sucrose, trehalose, albumin, as well as protease and/or nuclease antagonists.

“Physiological buffer solution” include but are not limited to sodium chloride solution, demineralized water, as well as suitable organic or inorganic buffer solutions such as but not limited to phosphate buffer, citrate buffer, tris buffer (tris(hydroxymethyl)aminomethane), HEPES buffer ([4 (2 hydroxyethyl)piperazino]ethanesulphonic acid) or MOPS buffer (3 morpholino-1 propanesulphonic acid). The choice of the respective buffer in general depends on the desired buffer molarity. Phosphate buffer are suitable, for example, for injection and infusion solutions.

In a sixth aspect the present invention relates to the isolated targeted delivery system of the first aspect of the present invention or producible according to the method of the second aspect of the invention for use in diagnosing tumours, preferably a solid tumour and/or its metastases, preferably breast cancer, pancreatic cancer, bladder cancer, lung cancer, colon cancer or its metastases, or a tumour having hypoxic areas, inflammatory disease or ischemic areas, in particular in skin wounds, other wounds, or after organ infarctus (heart) or ischemic retina.

The targeted delivery system according to the present invention enables tumour delivery of the labels, preferably contrast agents, which normally would not be able to reach the tumour (for example, due to solubility problems or lack of vasculature). It also enables the delivery of labels, preferably contrast agents to the hypoxic tumours or to the hypoxic areas of the tumour. This system also provides for delivery of a contrast agent to any area within an organism subjected to hypoxic conditions, for example during ischaemic incidents, or undergoing an inflammatory process.

As mentioned above the present invention provides also a method for targeted label delivery into the tumour mass. This method comprises preparation of CD45⁺ leukocytes which enables highly efficient label uptake or iron-binding protein (ferritin, haemoglobin and/or transferring) uptake by the macrophages, wherein said ferritin, haemoglobin and/or transferrin carry an label, preferably contrast agent and tumour targeting.

Additionally, the present invention allows for targeting radiolabels into the tumour mass. These methods comprise CD45+ leukocytes, preferably activated macrophages loaded with either ferritin-encapsulated or decorated with the contrast agent for MRI imaging (e.g. ferryhydrite) or PET/SPECT imaging (e.g. a or B radiation emitting radioisotope, which also emit a cell damaging amount of γ radiation, preferably selected from the group consisting of lutetium-177, ytterbium-90, iodine-131, samarium-153, phosphorus-32, caesium-131, palladium-103, radium-233, iodine-125, and boron-10 or a cell damaging amount of a radiation, preferably selected from the group consisting of actinium-225, bismuth-213, lead-212, and polonium-212).

The present invention exploits CD45⁺ leukocytes, preferably activated macrophages loaded with iron-binding proteins linked with a label, preferably contrast agent as a delivery system to target the tumour. Alternatively, CD45⁺ leukocytes, preferably activated macrophages labelled with the label, preferably contrast agent constitute the delivery label system to target the tumour and be visualised using imaging methods (e.g. PET). Difficulties in their detection using imaging methods are mainly related to an altered penetration of the contrast agents to the hypoxic areas observed mostly in solid tumours, especially their micrometastases due to poor vasculature. However, these avascular regions attract CD45⁺ leukocytes, preferably activated macrophages to migrate even in areas far away from blood vessels. Therefore, they constitute a delivery system of particles to the tumour mass. A promising example of such particles is iron-binding protein. However, when used as single agents they do not reach hypoxic regions, similarly to other compounds and accumulate in other organs.

The present inventors linked labels, or isotopes to haemoglobin or transferrin using chemical methods and loaded it into CD45⁺ leukocytes (monocytes, macrophages, lymphocytes and/or granulocytes), preferably activated macrophages treating cells with iron-binding protein solution as it is described in examples. The inventors observed that upon administration to the animal, loaded CD45⁺ leukocytes, preferably activated macrophages migrate to the tumour hypoxic sites and release iron-binding protein with encapsulated labels into the cancer cells. This method allows precise administration of the labels to the tumour site (especially to the hypoxic regions), avoiding their accumulation in other organs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1: Panel (A) shows a minimal active fragment of a consensus amino acid sequence among mammalian ferritin H chains and two full length consensus sequences based on several mammalian ferritin H chains (see SEQ ID NO: 1, 2 and 7, respectively) as well as a minimal and full length amino acid sequence of mouse (SEQ ID NO: 3 and 4) and human (SEQ ID NO: 5 and 6) ferritin H chain. Panel (B) shows a a minimal active fragment of a consensus amino acid sequence among mammalian ferritin L chains and two full length consensus sequences based on several mammalian ferritin L chains (see SEQ ID NO: 8, 9 and 14, respectively) as well as a minimal and full length amino acid sequence of mouse (SEQ ID NO: 10 and 11) and human (SEQ ID NO: 12 and 13) ferritin L chain. . Panel (C) shows a minimal active fragment of a consensus amino acid sequence among mammalian haemoglobin alpha chains and one full length consensus sequences based on several mammalian haemoglobin alpha chain (see SEQ ID NO: 15 and 16, respectively) as well as a minimal and full length amino acid sequence of human (SEQ ID NO: 17 and 18) haemoglobin alpha chain. Panel (D) shows a minimal active fragment of a consensus amino acid sequence among mammalian haemoglobin beta chains and a full length consensus sequences based on several mammalian haemoglobin beta chain (see SEQ ID NO: 19 and 20, respectively) as well as a minimal and full length amino acid sequence of human (SEQ ID NO: 21 and 22) haemoglobin beta chain. Panel (E) shows a N- and C-terminal minimal active fragment of a consensus amino acid sequence among mammalian transferrins (SEQ ID NO: 23 and 24) and a full length consensus sequences based on several mammalian transferrins (SEQ ID NO: 25) as well as a N- and C-terminal minimal active fragment of a human transferrin (SEQ ID NO: 26 and 27) and full length amino acid sequence of human transferrin (SEQ ID NO: 28). In the consensus sequences X indicates a position that is variable and stands for any natural amino acid. Preferably, in each case X in dependently of other X stands for the amino acid present in the human protein.

FIG. 2: Shows macrophage inside the mouse tumour mass (TRITC stained before injection, loaded with FITC-decorated ferritin).

FIG. 3: Shows confocal microscopy image of tumour tissue mouse injected with mammary cancer cells and given i.v. macrophages loaded with FITC-ferritin (asterix)—it is clearly observed, not only in macrophages but also in cancer cells, that ferritin-FITC spread within all tumour mass.

FIG. 4: Shows MRI images of mouse mammary tumour. The mouse was treated (at time point 0 h) with macrophages (i.v. injection) loaded with ferritin Fh. Then we observed increased diameter of blood vessels (arrow) filled with injected macrophages (giving significant T2-signal reduction) and afterword macrophages spread to the tissue (spot-like pattern; arrows). These changes (in the same time points) were observed in all examined mice.

FIG. 5: Shows ferritin, haemoglobin and transferrin uptake by macrophages, ferritin and haemoglobin uptake by monocytes and ferritin uptake by lymphocytes and granulocytes.

FIG. 6: Shows the stability of the ferritin storage by macrophages.

FIG. 7: Shows the picture from two-photon microscopy showing tumour from a mouse that received pre-labeled (before administration) macrophages containing Ferritin-FITC.

FIG. 8: Shows the whole body imaging of mice that intravenously received labeled macrophages, showing their accumulation in the tumour site and their distribution in other organs.

FIG. 9: Shows the migration of macrophages to hypoxic tissue, a cross-section of the tumour from a mouse that was administered intravenously with pre-labeled macrophages, tumour hypoxic areas are visualized with a hypoxia marker—pimonidazolone.

FIG. 10: Shows the signal recorded by PET from a whole-body analysis of mice with the metastatic 4T1 cancer. Mice received intravenously macrophages loaded with 18F-FDG. Signal accumulation is increased in the lungs of mice with micrometastases (confirmed by pathology examination). Mice receiving plain 18F-FDG, or mice without 4T1 cancer had lower PET signal.

EXAMPLE SECTION Example 1 Activation of Macrophages

Macrophages for use according to the present invention were obtained, differentiated and activated as follows. In order to activate macrophages, they are obtained firstly from bone marrow precursors (for example see paper: Weischenfeld and Porse, 2008, CSH Protoc, doi. 10.1101/pdb.prot.5080) or blood monocytes. Alternatively, they can be obtained from peritoneum. The methods of macrophage isolation, culture, differentiation and polarization/activation are well known for those skilled in the art. For example, they have been described in details by Murray et al. (Immunity, 2014, 41(1):14-20).

In this practical realization of the invention bone marrow derived macrophages were obtained from BALB/c or C57Bl/6 mouse, however canine blood-monocyte-derived macrophages or commercially available macrophage cell lines (monocyte-macrophage lineage mouse cells: RAW 264.7, J744, human cells: THP-1, U937, or canine cells DH82).

Shortly, such bone marrow derived macrophages are seeded in plastic Petri dish in 5 ml medium (3 ml cells per plate): DMEM:F12+glutamine/glutamax+10% FBS+Penicillin/Streptomycin and 20% of L929 conditioned medium or M-CSF (50 ng/ml). In the next five days the medium is supplemented in growth factor and one of the activating compounds or their combinations as one cytokine cocktail.

Alternatively, macrophages have been cultured in “M1/M2 Macrophage Generation Medium” (Promocell) or equivalent commercially available or self-made medium containing all the necessary cytokines and interleukins to consider them as activated.

In order to obtain macrophages from blood monocytes, fresh blood (not older than 12 hours) is spin down using Histopaque system 1077 or equivalent and white blood cells (or alternatively, only white blood cells collected from the blood bank) in an appropriate amount of pre-warmed Monocyte Attachment Medium (or equivalent, e.g. DMEM/RPMI supplemented with M-CSF), e.g. 15 ml Medium per T-75 flask. A seeding density should be of 1-2 million/cm² for mononuclear cells with a monocyte content of ≥25% and 1.5-3 million/cm2 for a monocyte content of <25%. Then, cells are incubated for 1 - 1.5 hours at 5% CO₂ and 37° C. in the incubator without any further manipulation.

After cell attachment, they are washed at least twice, and then an appropriate amount of complete “M1- or M2-Macrophage Generation Medium DXF” is added to the cells (e.g. 20 ml per T-75 flask) and cells are incubated for 6 days at 37° C. and 5% CO₂ without medium change. In order to activate macrophages, the whole medium should be replaced with medium supplemented by activating compound.

Activating compounds used in this invention (for bone-marrow derived cells or to activate cells from monocyte-macrophage cell lines) are as follows: IL-4 (20 ng/ml), IFN-γ (at least 20 ng/ml), LPS (at least 10 ng/ml), IL-13 (at least 20 ng/ml), IL-10 (at least 20 ng/ml), dexamethason (at least 20 μg/ml), oxLDL (at least 20 ng/ml), TNF-α (20 ng/ml), TGF-β (20 ng/ml), cortisol (150-300 ng/ml) or their combinations as one cytokine cocktail. In order to obtain unactivated macrophages, the activating compound has not been added.

Reverse of the polarization/activation of macrophages (from classically activated to alternatively activated) can be reached for example by culture of macrophages in appropriate cytokines listed above for at least 48 hrs.

Example 2 Monocyte Isolation

In order to obtain monocytes in this practical realization of the invention bone marrow derived or spleen-derived monocytes were obtained from BALB/c or C57Bl/6 mouse, however canine blood monocyte or commercially available monocyte cell lines were used (monocyte-macrophage lineage mouse cells: RAW 264.7, J744, human: THP-1, U937, or canine DH82 cell line).

To obtain blood monocytes, fresh blood (not older than 12 hours) is spin down using Histopaque system 1077 or equivalent and white blood cells are seeded in an appropriate amount of pre-warmed Monocyte Attachment Medium (or equivalent, e.g. DMEM/RPMI supplemented with 20 ng/ml M-CSF), e.g. 15 ml Medium per T-75 flask. Alternatively, only white blood cells collected from the blood bank (buffy coat) may be used. A seeding density should be of 1-2 million/cm2 for mononuclear cells with a monocyte content of ≥25% and 1.5-3 million/cm2 for a monocyte content of <25%. Then, cells are incubated for 1-1.5 hours at 5% CO₂ and 37° C. in the incubator without any further manipulation. After cell attachment, they are washed at least twice, and adherent cells are considered as monocytes.

In order to obtain bone-marrow derived monocytes, in this practical realization of the invention bone marrow derived macrophages were obtained from BALB/c or C57Bl/6 mouse. Shortly, such bone marrow derived precursors are seeded in plastic Petri dish in 5 ml medium (3 ml cells per plate): DMEM:F12+glutamine/glutamax+10% FBS+Penicillin/Streptomycin and 20% of L929 conditioned medium or 20 ng/ml M-CSF. Two days later 5 ml of standard medium is added. Then, after two days 0.5 ml/plate L929 conditioned medium is added. Adherent cells are considered as monocytes.

In order to obtain spleen derived monocytes, in this practical realization of the invention, the spleen has been mechanically dissociated to obtain single cell suspension and passed through the 70 μm cell strainer. Cells were centrifuged and supernatant was removed. After erythrocyte lysis the monocytes were isolated using magnetic bead purification e.g. EasySep Mouse Monocyte Enrichment Kit protocol and appropriate magnet.

To obtain better effects of their protein loads and migration before use they may be pre-treated with macrophage activation stimuli: IL-4 (20 ng/ml), IFN-γ (at least 20 ng/ml), LPS (at least 10 ng/ml), IL-13 (at least 20 ng/ml), IL-10 (at least 20 ng/ml), dexamethason (at least 20 μg/ml), oxLDL (at least 20 ng/ml), TNF-α (20 ng/ml), TGF-β (20 ng/ml), cortisol (150-300 ng/ml) or their combinations as one cytokine cocktail.

Example 3 Granulocyte Isolation

To obtain granulocyte cells from blood, 9 parts of blood were diluted with 1 part of ACD buffer (containing 0.17 M d-glucose, 0.10 M citric acid, 0.11 M trisodium citrate). Blood from this step was further diluted with PBS at the 1:1 ratio and centrifuged. After removing plasma and buffy coat, remaining cells were mixed with PBS to 80% of the original volume from the first step (ACD-blood) and then diluted with cold distillated water at the ratio of 4:12. Then, 6 parts of 2.7% of NaCl solution were added and centrifuged. After removal of supernatant cells were resuspended in RPMI-1640 medium. These cell were considered as granulocytes.

Example 4 Lymphocyte Isolation

In order to obtain spleen derived lymphocytes, in this practical realization of the invention, the spleen has been mechanically dissociated to obtain single cell suspension and passed through the 70 μm cell strainer. Cell were centrifuged and supernatant was removed. After erythrocyte lysis the lymphocytes were isolated using magnetic bead purification e.g. EasySep Mouse CD4⁺ Enrichment Kit protocol and appropriate magnet.

Example 5 Preparation of Ferritin Complexes

In order to incorporate ferritins with the anticancer drug (e.g. classic drugs like cyclophosphamide, chlorambucil, melphalan, bendamustine, banoxantrone or hypoxia-activated prodrug like TH-302) or with the “imaging contrast agents” (e.g. ferrihydride or isotope) ferritins have to be prepared before macrophage treatment. Shortly, recombinant mouse proteins according to SEQ ID NO: 4 (FIG. 1) are obtained as follows. The expression vector pET-22b containing a synthetic gene encoding ferritin protein of SEQ ID NO: 4 was transformed into E. coli BL21 (DE3). E. coli culture was grown at 37° C. to OD600 0.6 in 1 L of Luria-Bertani broth (LB) added with ampicillin (100 mg/L). Protein expression was induced by addition of 1 mM isopropyl thio-b-D-galactoside (IPTG) and the culture was incubated overnight. Cells were harvested by centrifugation (15000 g for 15 min) and suspended in 20 mM Hepes (pH 7.5), 150 mM NaCl, 0.1 mg/mL DNase, 10 mM MgCl₂ and disrupted by sonication. The lysate was centrifuged at 15000 g for 30 min and the supernatant was treated 10 min at 50° C., centrifuged to remove denatured proteins and then at 70° C. for 10 min and centrifuged again. The supernatant was added with 30% (NH)₄SO₄ at 4° C. stiffing for 1 h and centrifuged at 15000 g for 30 min. The supernatant was added with 70% (NH)₄SO₄ at 4° C. stirring for 1 h and centrifuged at 15000 g for 30 min. The pellet was resuspended in 20 mM Hepes (pH 7.5), 150 mM NaCl and dialysed overnight at 4° C. against the same buffer. The protein was loaded on a HILOAD 26/600 SUPERDEX 200 gel-filtration column (GE-Healthcare) and then sterile filtered and stored at 4° C. (FIG. 9) Protein concentration was determined spectrophotometrically at 280 nm using a molar extinction coefficient of 21000 M⁻¹ m⁻¹ and by Bradford assay measuring the absorbance at 595 nm.

Said ferritins include recombinant mammalian ferritin proteins H and/or L homopolymers.

Ferritins, obtained as previously described, are purified by standard methods in order to obtain an endotoxin free, pre-clinical grade product (see, for example: Ceci et al. 2011, Extremophiles 15(3):431-439; Vanucci et al. 2012, Int J Nanomed 7:1489-1509). Shortly, the ferritin conserved sterile in a storage solution containing 20 mM Hepes pH 7.5 is diluted to a final concentration of 4 uM in 24-mer in acidic solution (final pH<3.0) or, alternatively, at highly basic pH values (pH>9.5) (see for example Pontillo et al., 2016), thus allowing the dissociation of multimer. Drugs are dissolved at very high concentrations in the appropriate solvent and then a small volume is added to the ferritin solution with a 200 molar excess. PH is then brought to neutrality by addition of appropriate amounts of NaOH/HCl solutions in order to allow multimer reconstitution. Current experimental methods indicate that three/four washings using PBS (concentration steps) in 100 kDa cut off concentrators allows rapid and complete elimination both the co-solvents as well as non-encapsulated drugs and full recovery of drug loaded ferritin nanocages. The ferritin-drug complex thus obtained was then flash freezed in liquid nitrogen and lyophilised.

Depending on the choice of co-solvent and on the intrinsic chemical properties of the drug molecule, it can be estimated that up to 150-180 drug molecules can be entrapped/adsorbed within the 24-mer ferritin cage.

Labels may also be covalently coupled to ferritin amino acid side chains (lysines or cysteines) by appropriate choice of phenylhydrazone, succinimide or maleimide activated labesl. Accordingly, i) phenylhydrazone derivative may breaks and liberates the label from the ferritin surface, ii) lysine bound derivatives may become active after full protein degradation into aminoacids or iii) cysteine bound derivative may be liberated within the cell through reductive hydrolysis of the maleimede thioether link.

Example 6 Preparation of Haemoglobin-Compound Complex

Human haemoglobin is prepared from fresh red cells as described in Rossi-Fanelli et al. (Archives of biochemistry and biophysics 77:478-492, 1958). Shortly, the heparinized blood, obtained from healthy donors, was centrifuged at 1600 rpm for 30 minutes (4° C.) to sediment the RBCs. Buffy coat was accurately removed by needle aspiration on the surface of the pellet. The plasma supernatant was discarded and the RBC pellet was washed three times by resuspending the RBCs in isotonic 0.9% saline solution and centrifuging at 1600 rpm for 30 minutes at 4° C. After the final saline wash and centrifugation step, the RBC pellet was resuspended in distilled water buffered at pH 7.2 with 5 mM potassium phosphate buffer (PB, pH=7.2) and allowed to lyse at 4° C. overnight under gentle stirring. Dialyzed RBC lysate was subsequently centrifuged at 13.000 rpm for 30 min at 4° C. and supernatant was directly loaded on an AKTA Explorer system equipped with an XK 26/40 column packed with Q-sepharose XL resin (GE Healthcare) at room temperature. Columns were equilibrated with buffer A (20 mM Tris-HCl, pH=8.2) at a flow rate of 12 mL/min and washed three times with the same buffer. A linear gradient elution was generated by changing from 100% buffer A to 75% buffer B (20 mM Tris-Cl, plus 0.2 M NaCl pH8.20) followed by a step gradient of 100% buffer B. Upon elution, a fraction collector was used to collect protein fractions. Protein thus obtained was analyzed by SDS page and stored frozen at −80° C.

Human Haemoglobin (SEQ ID NO: 18 or 22, see FIG. 1) can be readily covalently linked to appropriate drug conjugates, host hydrophobic drug molecules within the heme binding pocket or even transport small cytotoxic molecules linked to the heme iron. Hb can be easily modified by selective attachment of the appropriate drug conjugate to the cysteine residue in position 93 of the beta chains, the only titratable cystein on the protein surface. The apo-protein solution must be kept at ice bath for the duration of the reconstitution process. A 1.5-fold molar excess of CuT-CPP (Cu-TCPP 4,4′,4″,4′″-(Porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid)-Cu⁶⁷) in 0.1 M NaOH must be added dropwise to the apo-globin solution in 0.2 M KPi buffer at pH 7.0 vortexed quickly at room temperature and then placed back in ice bath for 30 minutes. The protein solution must then be filtered in a syringe filter before use.

Example 7 Preparation of Transferrin-Compound Complex

The serum was obtained from healthy donor and excess iron was added in the presence of citrate ions as a chelator and bicarbonate, which is facilitates for iron binding to transferrin. The reaction mixture contained 6.5 mg sodium bicarbonate and 153.16 ferric citrate in pH=8, 4° C., 1 h per 100 mL of serum. Albumin was subsequently precipitated by Rivanol (4%) by adding the alcohol solution to the serum sample in a 3.5 V/V ratio at 4° C., and pH=9.4 for 2 h. Then, the solution was centrifuged at 3000 rpm for 20 min and finally filtered by filter on a 0.8 mm syringe filter. Excess Rivanol was subsequently removed by gel-filtration on a Sephadex G-25 column in ammonium sulfate 0.025 M. A first precipitation of by saturated ammonium sulfate 50% at pH=6.5 was subsequently carried out followed by centrifugation at 3000 rpm for 10 min (immunoglobulin removal). A second precipitation at 80% saturated ammonium sulfate was then carried out thus allowing recovery of transferrin the precipitate. Solid precipitate was then dissolved in buffer of 0.06 M Tris HCl buffer, pH=8, containing 1 M NaCl. The solution was dialyzed in the same buffer to allow full removal of ammonium sulfate. Protein solution was then concentrated with a centricon PM50 centrifugal concentrator up to 10-15 mg/ml (as estimated by Bradford method) and loaded on a Sephadex G-100 gel-filtration column (2,4×80 cm) equilibrated in 1M NaCl, flow rate of 15 ml/h. Transferrin thus obtained was estimated to be 88-90% pure by SDS page. Ion-exchange chromatography by anion exchanger DEAE Sephadex A-50 was then used as a final polishing step. The transferrin sample was loaded in the column equilibrated with 0.06 M Tris HCl at pH=8 and eluted by a linear concentration gradient with elution buffer, 0.3 M Tris HCl, pH=8. Protein purity was higher than 98% with a yield of about 150 mg per 100 mL of serum.

Human Holo-transferrin, (SEQ ID NO: 28, FIG. 1) similarly to haemoglobin can be readily covalently linked to appropriate label conjugates. The apo-protein solution must be kept at ice bath for the duration of the reconstitution process. A 1.5-fold molar excess of CuT-CPP (Cu-TCPP 4,4′,4″,4′″-(Porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid)-Cu⁶⁷) in 0.1 M NaOH must be added dropwise to the apo-globin solution in 0.2 M KPi buffer at pH 7.0 vortexed quickly at room temperature and then placed back in ice bath for 30 minutes. The protein solution must then be filtered in a syringe filter before use.

Example 8 Obtaining Ferritin Loaded Cells

Obtained cells are incubated in ferritin solution for a time and at the concentration sufficient to ensure proper ratio of ferritin/cell for their full load and also to ensure proper contrast content to obtain proper imaging). The time and concentration may vary depending on the number of molecules encapsulated/adsorbed into the ferritin cage, status of cell activation, condition and number of their intended administration.

For example, to ensure proper load with ferritins, cells are incubated for 1-4 hrs in ferritin solution 0.2 mg/ml in standard culture conditions. The frame of ferritin concentration may vary at least between 0.01 and 4 mg/ml as well as incubation time (5 min-6 hrs or more). Adjusting time and concentration of ferritin load to cells, the influence of ferritin and treatment conditions on cell viability should be minded. Cells obtained as stated above very easily uptake ferritins in a relatively short time (in minutes; FIG. 5). Once they absorb ferritins, they do not release it to the culture medium (FIG. 6).

Nevertheless, the person skilled in the art is able to re-adjust the above conditions and optimize the protocol for the own purposes in the own laboratory.

Example 9 Obtaining Haemoglobin Loaded Cells

Obtained cells are incubated in haemoglobin solution for a time and at the concentration sufficient to ensure proper ratio of haemoglobin/cell for their full load and also to ensure proper contrast content to obtain proper imaging. The time and concentration may vary depending on the number of molecules linked with the haemoglobin molecule, status of cell activation, condition and number of their intended administration.

For example, to ensure proper load with haemoglobins, cells are incubated for 1-4 hrs in haemoglobin solution 0.1 mg/ml in standard culture conditions. The frame of haemoglobin concentration may vary at least between 0.01 and 0.2 mg/ml as well as incubation time (5 min-4 hrs or more). Adjusting time and concentration of haemoglobin load to cells, the influence of ferritin and treatment conditions on cell viability should be minded. Cells obtained as stated above very easily uptake haemoglobins in a relatively short time (in minutes; FIG. 5).

Nevertheless, the person skilled in the art is able to re-adjust the above conditions and optimize the protocol for the own purposes in the own laboratory.

Example 10 Obtaining Transferrin Loaded Cells

Obtained cells are incubated in transferrin solution for a time and at the concentration sufficient to ensure proper ratio of transferrin/cell for their full load and also to ensure proper contrast content to obtain proper imaging. The time and concentration may vary depending on the number of molecules linked with the transferrin molecule, status of cell activation, condition and number of their intended administration.

For example, to ensure proper load with transferrins, cells are incubated for 1-4 hrs in transferrin solution 0.1 mg/ml in standard culture conditions. The frame of transferrin concentration may vary at least between 0.01 and 0.2 mg/ml as well as incubation time (5 min-4 hrs or more). Adjusting time and concentration of transferrin load to cells, the influence of transferrin and treatment conditions on cell viability should be minded. Cells obtained as stated above very easily uptake transferrin in a relatively short time (in minutes; FIG. 5).

Nevertheless, the person skilled in the art is able to re-adjust the above conditions and optimize the protocol for the own purposes in the own laboratory.

Example 11 Cell Labeling With Radioisotope

In this invention cells were labeled with ¹⁸F-FDG in order to become imaged on PET. Cells have been detached from the plate and incubated with ¹⁸F-FDG solution in adequate concentration to ensure the most optimal ¹⁸F-FDG uptake by cells allowing their radio-detection at the site of their accumulation. In this practical invention cells were pre-treated with various cytokine cocktails, growth factors and other factors influencing their activation state to enhance their uptake of label and incubated in the warm ¹⁸F-FDG solution containing 20-60 MBq. After labeling, cells should be centrifuged and supernatant should be removed. This step should be repeated until no radioactivity is detected in the supernatant.

Example 12 Ferritin/Haemoglobin/Transferrin/Label-Leukocyte Complex as Useful Delivery Tool to Tumor

The macrophages from Example 1 prepared as described in Examples 8, 9, 10 and 11; monocytes from Example 2 prepared as described in Examples 8, 9, 10 and 11, granulocytes from Example 3 prepared as described in Examples 8, 9, 10 and 11, and lymphocytes from Example 4 prepared as described in Examples 8, 9, 10 and 11, very easily transport ferritins, haemoglobins, transferrins and labels to the tumor in the enough amount to be detected using imaging systems (FIGS. 2, 3, 4, 7, and 8).

Example 13 Leukocyte-Protein Carrier Complex as Useful Targeted Drug Delivery Agent to Hypoxic Regions

Macrophages prepared as above are injected into the tail vein of animal with the tumour (appropriate number of macrophages should be adjusted to the tumour size, stage of development and presence of metastases). As it is shown on FIGS. 2, 3, 4, 7, 8 and 10 they specifically reach the tumour (after a few hrs) and also disperse in other organs of the whole animal. Moreover, as it is shown on FIG. 9, in hypoxic model they are also able to migrate to the avascular and hypoxic sites.

For the imaging purposes, 1-50 millions of macrophages were injected into the tail vein of mammary or colon cancer tumour-bearing animal. Before, macrophages were pre-labeled with Cell Tracker and loaded with ferritin-FITC (as shown in Example 8). Using two-photon imaging of the tumour mass 8 hrs after administration of macrophages the presence of macrophages carrying Ferritin-FITC was detected (FIG. 7). Their specific targeting of tumour but also their migration to other organs was shown using whole animal body imaging (IVIS) after macrophage pre-labeling using XenoLight DiR lipophilic DIR cytoplasmic dye (FIG. 8).

Example 14 Leukocyte-Protein Carrier Complex or Labeled Leukocyte as Useful Imaging Tool

The targeted delivery system described in present invention constitutes very useful imaging tool. As it is presented on FIGS. 4 and 10, after injection of 1-50 ml of macrophages loaded with ferritin coupled as described in Example 8 with a contrast agent (in this example: ferrihydrite, however the same results are obtained with isotope, e.g. ¹²³I) or labeled with isotope (in this case ¹⁸F-FDG) (FIG. 10) they can be easily detected by MRI, PET or SPECT. In this example (FIG. 4), mammary-tumour bearing mice were imaged using MRI at 3, 22 and 24 hours after i.v. injection of macrophages loaded with ferritin Fh. As it is shown on FIG. 4 the ferritin/macrophage complex is very useful imaging tool. The mouse was treated (at time point 0 h) with macrophages. Then increased diameter of blood vessels (arrow) filled with injected macrophages (giving significant T2-signal reduction) has been observed and afterword macrophages spread to the tissue (spot-like pattern; arrows). These changes (in the same time points) were observed in all examined mice.

Macrophages were also labeled with ¹⁸F-FDG (1-50 min) and imaged using PET at 1 h after i.v. administration to the tumour-bearing mice. These mice were inoculated with 4T1 metastatic cell line 3 weeks before the experiment and metastases in the lungs, liver and spleen were histopatologically confirmed. At FIG. 10 it is seen that macrophages migrated to the regions with metastatic tumours allowing their visualization at PET.

While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.

The present invention also relates to the following aspects and preferred embodiments of these aspects. The definitions provided above similarly apply to below aspects and embodiments.

-   -   1. Targeted delivery system comprising an activated macrophage         loaded with ferritin carrying a contrast agent.     -   2. The targeted delivery system according to embodiment 1,         wherein the contrast agent is a ferrihydride or an isotope.     -   3. Method of preparation of the targeted delivery system         comprising an activated macrophage loaded with ferritin carrying         a contrast agent comprising steps of         -   a) ferritin purification;         -   b) obtaining ferritin carrying a contrast agent by linking             of ferritin with said contrast agent;         -   c) activation of isolated macrophages;         -   d) incubation of macrophages in solution of ferritin             carrying a contrast agent as obtained in step b) for a time             and at the ferritin concentration sufficient to ensure full             load of ferritin carrying a contrast agent into macrophages.     -   4. The method of embodiment 3, wherein activated macrophages are         bone marrow originated macrophages.     -   5. The method of embodiment 3, wherein activated macrophages are         blood originated macrophages.     -   6. The method of embodiment 3, wherein activated macrophages are         derived from macrophage cell lines.     -   7. The method of any one of embodiments 3-6, wherein activated         macrophages are macrophages polarized towards M1 or M2.     -   8. The method of embodiment 7 wherein activated macrophages have         been polarized towards M2.     -   9. The method of embodiment 7 wherein activated macrophages have         been manipulated with respect to iron metabolism.     -   10. The method of any one of embodiments 3-9, wherein the         contrast agent is a ferrihydride or an isotope.     -   11. Targeted delivery system as defined in any of embodiments 1         or 2 for use as imaging tool.

In a preferred embodiment the present invention does not comprise the subject-matter of items 1 to 11 above. 

1. An isolated targeted delivery system comprising a CD45⁺ leukocyte cell comprising within said cell a complex of one or more iron binding proteins and aft label.
 2. An isolated targeted delivery system comprising a CD45⁺ leukocyte cell comprising one or more label.
 3. The isolated targeted delivery system according to claim 1, wherein the leukocyte cell is producible from a CD34⁺ hematopoietic precursor cell.
 4. The isolated targeted delivery system according to claim 1, wherein the leukocyte is selected from the group consisting of a monocyte, a differentiated monocyte, lymphocyte and a granulocyte.
 5. The isolated targeted delivery system according to claim 4, wherein (i) the monocyte is a CD11b⁺ monocyte; (ii) the differentiated monocyte is selected from the group consisting of a macrophage, an activated macrophage, preferably a CD11b⁺ macrophage, more preferably a CD11b⁺ CD16⁺ macrophage, CD11b⁺ CD32⁺ macrophage, CD11b⁺ CD64⁺ macrophage, CD11b⁺ CD68⁺ macrophage, preferably a CD11b⁺ CD86⁺ M1 macrophage, preferably producing iNOS and/or secreting interleukin 12 (IL-12) or preferably CD11b⁺ CCR2⁺ M2 macrophage, CD11b⁺ CD204⁺ M2 macrophage, CD11b⁺ CD206⁺ M2 macrophage, CD11b⁺ CD204⁺ CD206⁺ M2 macrophage, CD11b⁺ Mayor Histocompatibility Complex II⁺ (MHCII⁺) (low or hi expression) M2 macrophage, CD11b⁺ CD200R⁺ M2 macrophage, CD11b⁺ CD163⁺ M2 macrophage or activated macrophage producing arginase and/or secreting interleukin 10 (IL-10); or a dendritic cell; (iii) monocyte or activated monocyte expressing of at least one chemokine receptor, or at least one growth factor receptor; (iv) the lymphocyte is selected from the group consisting of a CD3⁺ and CD4⁺ or CD8⁺ T lymphocyte, or a CD19⁺, CD20⁺, CD21⁺, CD19⁺ CD20⁺, CD19⁺ CD21⁺, CD20⁺ CD21⁺, or CD19⁺ CD20⁺ CD21⁺ B lymphocyte; or (v) the granulocyte is selected from the group consisting of a neutrophil, an eosinophil and a basophil.
 6. The isolated targeted delivery system of claim 5, wherein the leukocyte is a differentiated monocyte, and wherein the differentiated monocyte is an activated macrophage, wherein the activated macrophage: (i) is producible by in vitro incubation of a monocyte or macrophage with a factor capable of altering expression markers on macrophages, (ii) is characterized by expression of at least one of following antigens: CD64, CD86, CD16, CD32, high expression of MHCII, and/or production of iNOS and/or IL-12; (iii) is producible by in vitro incubation of a monocyte or macrophage with a factor capable of inducing the ability of the macrophage to phagocytose; (iv) is characterized by expression of at least one of following antigens: CD204, CD206, CD200R; CCR2, transferrin receptor (TfR), CXC-motive chemokine receptor 4 (CXCR4), CD163, and/or T cell immunoglobulin-domain and mucin-domain 2 (TIM-2), and/or show low expression of MHCII; (v) has the ability to phagocytose; and/or (vi) is capable of cytokine secretion, or production of inducible nitric oxide synthetase (iNOS) (or other pro-inflammatory compounds), arginase or other immunosuppressive/anti-inflammatory compounds.
 7. The targeted delivery system according to claim 6, wherein: (i) the M1 inducer is selected from the group consisting of LPS, INF-γ, GM-CSF and viral and bacterial infection; or (ii) the M2 inducer is selected from the group consisting of IL-4, IL-10, IL-13, immune complex of an antigen and antibody, IgG, heat activated gamma-globulin, glucocorticosteroid, TGF-β, IL-1R, CCL-2, IL-6, M-CSF, PPARγ agonist, Leukocyte inhibitory factor, adenosine, helminth and fungal infection.
 8. The isolated targeted delivery system of claim 5, wherein the leukocyte is a monocyte, wherein the monocyte: (i) is producible from a CD34⁺ hematopoietic precursor cell; (ii) is producible by in vitro incubation of monocytes with at least one inducer; (iii) is characterized by expression of at least one of the following antigens: TfR⁺, CD163⁺, CD14⁺, CD16⁺, CD33⁺, and/or CD115⁺; (iv) is characterized by expression of at least one of the following antigens: TfR⁺, CD163⁺, CXCR4⁺, CD14⁺, and/or CD16⁺; and/or (v) has the ability to phagocytose.
 9. The targeted delivery system according to claim 8, wherein: (i) the M1 inducer is selected from the group consisting of LPS, INF-γ, GM-CSF or viral or bacterial infection; (ii) the M2 inducer is selected from the group consisting of IL-4, IL-10, IL-13, immune complex of an antigen and antibody, IgG, heat activated gamma-globulins, Glucocorticosteroids, TGF-β, IL-1R, CCL-2, IL-6, M-CSF, PPARγ agonist, Leukocyte inhibitory factor, cancer-conditioned medium, cancer cells, adenosine and helminth or fungal infection.
 10. The isolated targeted delivery system of claim 5, wherein the leukocyte is a lymphocyte, wherein the lymphocyte: (i) is obtainable from blood, spleen, or bone marrow or is producible from a CD34⁺ precursor cell; (ii) is an immunologically competent lymphocyte; (iii) expresses antigen specific T cell receptors; and/or (iv) is characterized by expression of at least one of the following antigens: (a) CD3⁺ and CD4⁺ or CD8⁺ or (b): CD19⁺, CD20⁺, CD21⁺, CD19⁺ CD20⁺, CD19⁺ CD21⁺, CD20⁺ CD21⁺, or CD19⁺ CD20⁺ CD21⁺ antigen.
 11. The isolated targeted delivery system of claim 5, wherein the leukocyte is a granulocyte, wherein the granulocyte: (i) is obtainable from blood, spleen or bone marrow or producible from a CD34⁺ precursor cell; (ii) is characterized by expression of at least one of the following CD66b⁺ and/or CD193⁺; (iii) is a polymorphonuclear leukocyte characterized by the presence of granules in their cytoplasm; and/or (iii) is characterized by expression of at least one of the following: TfR⁺, CD163⁺, TIM-2⁺, and/or CXCR4⁺.
 12. The isolated targeted delivery system of claim 1, wherein the iron binding protein is selected from the group consisting of ferritin; haemoglobin, haemoglobin-haptoglobin complex, hemopexin, transferrin; and lactoferrin.
 13. The isolated targeted delivery system of claim 1, wherein the label is selected from a fluorescent dye, a fluorescence emitting isotope, a radioisotope, a detectable polypeptid or nucleic acid encoding a detectable polypeptide and a contrast agent.
 14. The isolated targeted delivery system of claim 1, wherein the label comprises a chelating agent which forms a complex with divalent or trivalent metal cations.
 15. The isolated targeted delivery system of claim 14, wherein the chelating agent is selected from the group consisting of 1,4,7,10-tetraazacyclododecane-N,N′,N,N′-tetraacetic acid (DOTA), ethylenediaminetetraacetic acid (EDTA), 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), triethylenetetramine (TETA), iminodiacetic acid, Diethylenetriamine-N,N,N′,N′,N″-pentaacetic acid (DTPA) and 6-Hydrazinopyridine-3-carboxylic acid (HYNIC).
 16. The isolated targeted delivery system of claim 13, wherein the contrast agent comprises a paramagnetic agent, or ferrihydride.
 17. The isolated targeted delivery system of claim 13, wherein the radioisotope/fluorescence emitting isotope is selected from the group consisting of alpha radiation emitting isotopes, gamma radiation emitting isotopes, Auger electron emitting isotopes, X-ray emitting isotopes, fluorescent isotopes, fluorescence emitting isotopes, as well as conjugates and combinations of above with proteins, peptides, small molecular inhibitors, antibodies or other compounds.
 18. The isolated targeted delivery system of claim 13, wherein the fluorescence dye is selected from the group consisting of the following classes of fluorescent dyes: Xanthens, Acridines, Oxazines, Cynines, Styryl dyes, Coumarines, Porphines, Metal-Ligand-Complexes, Fluorescent proteins, Nanocrystals, Perylenes and Phtalocyanines as well as conjugates and combinations of these classes of dyes.
 19. The isolated targeted delivery system according to claim 13, wherein the detectable polypeptide is an autofluorescent protein, or any structural variant thereof with an altered adsorption and/or emission spectrum.
 20. The isolated targeted delivery system according to claim 1, wherein: (i) the bond(s) between the iron binding protein(s) and the label comprised in the complex are covalent and/or non-covalent; and/or (ii) the label comprised in the complex is entrapped/encapsulated by the iron binding protein or multimers thereof.
 21. The isolated targeted delivery system according to claim 2, wherein the label is directly or indirectly through a linker or spacer linked to the cell.
 22. Method of preparation of the isolated targeted delivery system of claim 1 comprising steps of a) providing purified iron binding protein; b) covalently or non-covalently linking a label to and/or encapsulating a label in an iron binding protein; c) providing a CD45⁺ leukocyte cell; and d1) incubating the CD45⁺ leukocyte cell in the presence of the complex of the iron binding protein and the label produced in step b) until the CD45⁺ leukocyte cell is at least partially loaded with the complex of the iron binding protein and the label produced in step b); and/or d2) incubating CD45⁺ leukocyte cell in the presence of the label until the CD45⁺ leukocyte cell is at least partially labelled with the label.
 23. The isolated targeted delivery system of claim 1 for use as a diagnostic.
 24. A diagnostic composition comprising the isolated targeted delivery system of claim 1 and a pharmaceutically acceptable carrier and/or suitable excipient(s).
 25. A isolated targeted delivery system of claim 1 for use in diagnosing tumours. 